Reflective mask blank, method of manufacturing reflective mask blank, reflective mask and method of manufacturing semiconductor device

ABSTRACT

Provided is a reflective mask blank capable of facilitating the discovery of contaminants, scratches and other critical defects by inhibiting the detection of pseudo defects attributable to surface roughness of a substrate or film in a defect inspection using a highly sensitive defect inspection apparatus. The reflective mask blank has a mask blank multilayer film comprising a multilayer reflective film, obtained by alternately laminating a high refractive index layer and a low refractive index layer, and an absorber film on a main surface of a mask blank substrate, wherein the root mean square roughness (Rms), obtained by measuring a 3 μm×3 μm region on the surface of the reflective mask blank on which the mask blank multilayer film is formed with an atomic force microscope, is not more than 0.5 nm and the power spectrum density at a spatial frequency of 1 μm −1  to 10 μm −1  is not more than 50 nm 4 .

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2014/072688 filed Aug. 29, 2014, claiming priority based onJapanese Patent Application No. 2013-179123 filed Aug. 30, 2013, thecontents of all of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a reflective mask blank that is able tofacilitate discovery of contaminants or scratches and other criticaldefects by inhibiting detection of pseudo defects attributable tosurface roughness of a substrate or film in a defect inspection using ahighly sensitive defect inspection apparatus, a method of manufacturingthe reflective mask blank, a reflective mask and a method ofmanufacturing a semiconductor device.

BACKGROUND ART

Accompanying the increasingly higher levels of integration ofsemiconductor devices in the semiconductor industry in recent years,there is a need for fine patterns that exceed the transfer limitationsof conventional photolithography methods using ultraviolet light.Extreme ultraviolet (EUV) lithography is considered to be promising asan exposure technology that uses EUV light to enable the formation ofsuch fine patterns. Here, EUV light refers to light in the wavelengthband of the soft X-ray region or vacuum ultraviolet region, and morespecifically, light having a wavelength of about 0.2 nm to 100 nm.Reflective masks have been proposed as transfer masks for use in thisEUV lithography. Such reflective masks have a multilayer reflective filmthat reflects exposure light formed on a substrate, and an absorber filmformed in a pattern on the multilayer reflective film that absorbsexposure light.

The reflective mask is manufactured from a substrate, a multilayerreflective film formed on the substrate, and a reflective mask blankhaving an absorber film formed on the multilayer reflective film, byforming an absorber film pattern by photolithography and the like.

As has been described above, due to the growing demand forminiaturization in the lithography process, significant problems arebeing encountered in the lithography process. One of these is theproblem relating to defect information of mask blank substrates,substrates with multilayer reflective films and reflective mask blanksand the like used in the lithography process.

Mask blank substrates are being required to have even higher smoothnessfrom the viewpoints of improving defect quality accompanying theminiaturization of patterns in recent years and the optical propertiesrequired of transfer masks.

In addition, substrates with multilayer reflective films are also beingrequired to have even higher smoothness from the viewpoints of improvingdefect quality accompanying the miniaturization of patterns in recentyears and the optical properties required of transfer masks. Multilayerreflective films are formed by alternately laminating layers having ahigh refractive index and layers having a low refractive index on thesurface of a mask blank substrate. Each of these layers is typicallyformed by sputtering using sputtering targets composed of the materialsthat form these layers.

Ion beam sputtering is preferably carried out for the sputtering methodfrom the viewpoint of not requiring the generation of plasma byelectrical discharge and being resistant to contamination by impuritiespresent in the multilayer reflective film, and from the viewpoint ofhaving an independent ion source thereby making setting of conditionscomparatively easy. In addition, from the viewpoint of the smoothnessand surface uniformity of each layer formed, the high refractive indexlayer and low refractive index layer are deposited by allowing sputteredparticles to reach the target at a large angle with respect to thenormal (line perpendicular to the main surface of the mask blanksubstrate) of a main surface of the mask blank substrate, or in otherwords, at an angle diagonal or nearly parallel to a main surface of thesubstrate.

Patent Literature 1 describes a technology for manufacturing a substratewith a multilayer reflective film using such a method in which, whendepositing a multilayer reflective film of a reflective mask blank forEUV lithography on a substrate, ion beam sputtering is carried out bymaintaining the absolute value of an angle α formed between the normalof the substrate and sputtered particles entering the substrate suchthat 35 degrees≦α≦80 degrees while rotating the substrate about thecentral axis thereof.

In addition, Patent Literature 2 describes a reflective mask blank forEUV lithography in which an absorber layer that absorbs EUV lightcontains Ta, B, Si and N, the content of B is not less than 1 at % toless than 5 at %, the content of Si is 1 at % to 25 at %, and thecomposition ratio between Ta and N (Ta:N) is 8:1 to 1:1.

PRIOR ART LITERATURE Patent Literature

Patent Literature 1: JP 2009-510711A

Patent Literature 2: JP 2007-311758A

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Accompanying the rapid pace of pattern miniaturization in lithographyusing EUV light, the defect size of reflective masks in the form of EUVmasks is becoming increasingly smaller year by year, and the inspectionlight source wavelengths used during defect inspections in order todiscover such fine defects are approaching the light source wavelengthof the exposure light.

For example, highly sensitive defect inspection apparatuses having aninspection wavelength of 266 nm (such as the “MAGICS M7360”Mask/Substrate/Blank Defect Inspection Apparatus for EUV Exposuremanufactured by Lasertec Corp.), an inspection wavelength of 193 nm(such as the “Teron 610” of “Teron 600 Series”, EUV Mask/Blank DefectInspection Apparatuses manufactured by KLA-Tencor Corp.), or aninspection wavelength of 13.5 nm are being used or proposed increasinglyfrequently as defect inspection apparatuses of EUV masks and mastersthereof in the form EUV mask blanks, substrates with multilayerreflective film and substrates.

In addition, in the case of multilayer reflective films of substrateswith multilayer reflective films used in conventional EUV masks,attempts have been made to reduce concave defects present on thesubstrate by depositing according to, for example, the method describedin Patent Literature 1. However, no matter how much defects attributableto concave defects in a substrate are able to be reduced, due to thehigh detection sensitivity of the aforementioned highly sensitive defectdetection apparatuses, there is still the problem of the number ofdetected defects (number of detected defects=number of criticaldefects+number of pseudo defects) being excessively large when a defectinspection is carried out on the multilayer reflective film.

In addition, problems in terms of depositing the absorber layer(absorber film) and problems with the reflectance of EUV light orinspection light have been attempted to be solved by employing acomposition ratio like that described in Patent Literature 2, forexample, for the absorber layer of a reflective mask blank used inconventional EUV masks. With respect to surface roughness of the surfaceof the absorber layer as well, smoothing is considered to be favorablefrom the viewpoint of preventing exacerbation of pattern dimensionalaccuracy. However, no matter how much deposition problems of theabsorber layer are able to be resolved, if a defect inspection iscarried out on an absorber layer using a highly sensitive defectinspection apparatus having high detection sensitivity as previouslydescribed, the problem results in which an excessively large number ofdefects are detected.

Pseudo defects as mentioned here refer to surface irregularities thatare permitted to be present on a substrate surface, multilayerreflective film or absorber layer and do not have an effect on patterntransfer, and end up being incorrectly assessed as defects in the caseof having been inspected with a highly sensitive defect inspectionapparatus. If a large number of such pseudo defects are detected in adefect inspection, critical defects that have an effect on patterntransfer end up being concealed by the large number of pseudo defects,thereby preventing critical defects from being discovered. For example,in the case of currently popular defect inspection apparatuses having aninspection light source wavelength of 266 nm or 193 nm, more than 50,000defects end up being detected in a substrate, substrate with amultilayer reflective film or reflective mask blank having a size of,for example, 132 mm×132 mm, thereby obstructing inspections for thepresence of critical defects. Overlooking critical defects in a defectinspection results in defective quality in the subsequent semiconductordevice volume production process and leads to unnecessary labor andeconomic losses.

With the foregoing in view, an object of the present invention is toprovide a reflective mask blank that is able to facilitate discovery ofcontaminants or scratches and other critical defects by inhibitingdetection of pseudo defects attributable to surface roughness of asubstrate or film in a defect inspection using a highly sensitive defectinspection apparatus, a method of manufacturing the reflective maskblank, a reflective mask and a method of manufacturing a semiconductordevice that uses that reflective mask.

In addition, an object of the present invention is to provide areflective mask blank that enables critical defects to be reliablydetected since the number of detected defects, including pseudo defects,is reduced even when using highly sensitive defect inspectionapparatuses that use light of various wavelengths, and achievessmoothness required by reflective mask blanks in particular whilesimultaneously reducing the number of detected defects, including pseudodefects, a method of manufacturing that reflective mask blank, areflective mask and a method of manufacturing a semiconductor devicethat uses that reflective mask.

Means for Solving the Problems

As a result of conducting extensive studies to solve the aforementionedproblems, the inventors of the present invention found that theroughness of a prescribed spatial frequency (or spatial wavelength)component has an effect on the inspection light source wavelength of ahighly sensitive defect inspection apparatus. Therefore, by specifyingthe spatial frequency of a roughness component at which a highlysensitive defect inspection apparatus ends up incorrectly assessing adefect as a pseudo defect among roughness (surface irregularity)components on the surface of a film (such as an absorber film) formed ona main surface of a substrate, and managing amplitude intensity at thatspatial frequency, detection of pseudo defects in a defect inspectioncan be inhibited and critical defects can be made more conspicuous.

In addition, although attempts have been made to reduce the surfaceroughness of reflective mask blanks in the past, there is no knowncorrelation whatsoever with the detection of pseudo defects by highlysensitive defect inspection apparatuses.

Therefore, the present invention has the configurations indicated belowin order to solve the aforementioned problems.

The present invention is a reflective mask blank characterized by thefollowing Configurations 1 to 6, a method of manufacturing a reflectivemask blank characterized by the following Configurations 7 to 16, areflective mask characterized by the following Configuration 17, and amethod of manufacturing a semiconductor device characterized by thefollowing Configuration 18.

(Configuration 1)

Configuration 1 of the present invention is a reflective mask blank,comprising: a mask blank multilayer film that comprises a multilayerreflective film, obtained by alternately laminating a high refractiveindex layer and a low refractive index layer, and an absorber film on orabove a main surface of a mask blank substrate; wherein, the root meansquare roughness (Rms), obtained by measuring a 3 μm×3 μm region on asurface of the reflective mask blank on which the mask blank multilayerfilm is formed with an atomic force microscope, is not more than 0.5 nmand the power spectrum density at a spatial frequency of 1 μm⁻¹ to 10μm⁻¹ is not more than 50 nm⁴.

According to Configuration 1, by making the root mean square roughness(Rms) on the surface of the reflective mask blank to be not more than0.5 nm, and by making the power spectrum density, which is the amplitudeintensity of all roughness components detectable in a 3 μm×3 μm regionat a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹, to be not more than 50 nm⁴,detection of pseudo defects in a defect inspection using a highlysensitive defect inspection apparatus can be inhibited while makingcritical defects more conspicuous.

(Configuration 2)

Configuration 2 of the present invention is the reflective mask blankdescribed in Configuration 1, wherein the mask blank multilayer filmfurther comprises a protective film arranged in contact with a surfaceof the multilayer reflective film on the opposite side from the maskblank substrate.

According to Configuration 2, since damage to the surface of themultilayer reflective film can be inhibited when fabricating a transfermask (EUV mask) as a result of the reflective mask blank having aprotective film on the multilayer reflective film, reflectanceproperties with respect to EUV light can be further improved. Inaddition, in a reflective mask blank, since detection of pseudo defectsin a defect inspection of the surface of the protective film using ahighly sensitive defect inspection apparatus can be inhibited, criticaldefects can be made to be more conspicuous.

(Configuration 3)

Configuration 3 of the present invention is the reflective mask blankdescribed in Configuration 1 or Configuration 2, wherein the mask blankmultilayer film further comprises an etching mask film arranged incontact with the surface of the absorber film on the opposite side fromthe mask blank substrate.

According to Configuration 3, by using an etching mask film havingdifferent dry etching properties from those of the absorber film, ahighly precise transfer pattern can be formed when forming a transferpattern on the absorber film.

(Configuration 4)

Configuration 4 of the present invention is the reflective mask blankdescribed in any of Configurations 1 to 3, wherein the absorber filmcomprises tantalum and nitrogen, and the nitrogen content is 10 at % to50 at %.

According to Configuration 4, as a result of the absorber filmcomprising tantalum and nitrogen and the nitrogen content thereof being10 at % to 50 at %, the root mean square roughness (Rms) of the surfaceof the absorber film, and the power spectrum density, which is theamplitude intensity of all roughness components detectable in a 3 μm×3μm region at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹, are within theprescribed ranges, and pattern edge roughness when patterning theabsorber film can be reduced since enlargement of crystal grainscomposing the absorber film can be inhibited.

(Configuration 5)

Configuration 5 of the present invention is the reflective mask blankdescribed in any of Configurations 1 to 4, wherein the film thickness ofthe absorber film is not more than 60 nm.

According to Configuration 5, by making the film thickness of theabsorber film to be not more than 60 nm, in addition to being able toreduce shadowing effects, the root mean square roughness (Rms) of thesurface of the absorber film, and the power spectrum density, which isthe amplitude intensity of all roughness components detectable in a 3μm×3 μm region at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹, can befurther reduced. As a result thereof, a reflective mask blank isobtained that is able to inhibit the detection of pseudo defects in adefect inspection using a highly sensitive defect inspection apparatus.

(Configuration 6)

Configuration 6 of the present invention is the reflective mask blankdescribed in any of Configurations 1 to 5, wherein the absorber film hasa phase shift function by which the phase difference between lightreflected from the surface of the absorber film and light reflected fromthe surface of the multilayer reflective film or protective film wherethe absorber film is not formed has a prescribed phase difference.

According to Configuration 6, as a result of the absorber film having afunction by which the phase difference between reflected light from thesurface of the absorber film and reflected light from the surface of themultilayer reflective film or protective film where the absorber film isnot formed has a prescribed phase difference, a master for a reflectivemask in the form of a reflective mask blank is obtained thatdemonstrates improved transfer resolution by EUV light. In addition,since the film thickness of the absorber film required to demonstratephase shift effects needed to obtain a desired transfer resolution canbe reduced in comparison with the prior art, a reflective mask blank isobtained that exhibits reduced shadowing effects.

(Configuration 7)

Configuration 7 of the present invention is a method of manufacturing areflective mask blank having a mask blank multilayer film, comprising amultilayer reflective film and an absorber film on or above a mainsurface of a mask blank substrate, wherein a multilayer reflective filmis obtained by alternately laminating a high refractive index layer anda low refractive index layer, the method comprising: forming themultilayer reflective film on or above the main surface of the maskblank substrate, and forming the absorber film on or above themultilayer reflective film; wherein, the absorber film is formed so thata surface of the reflective mask blank has a root mean square roughness(Rms), obtained by measuring a 3 μm×3 μm region with an atomic forcemicroscope, of not more than 0.5 nm and a power spectrum density at aspatial frequency of 1 μm⁻¹ to 10 μm⁻¹ of not more than 50 nm⁴.

According to Configuration 7, as a result of making the surface of areflective mask blank to have an Rms of not more than 0.5 nm and thepower spectrum density, which is the amplitude intensity of allroughness components detectable in a 3 μm×3 μm region at a spatialfrequency of 1 μm⁻¹ to 10 μm⁻¹, of not more than 50 nm⁴, a reflectivemask blank can be fabricated that is capable of inhibiting the detectionof pseudo defects in a defect inspection using a highly sensitive defectinspection apparatus and making critical defects more conspicuous.

(Configuration 8)

Configuration 8 of the present invention is the method of manufacturinga reflective mask blank described in Configuration 7, wherein, when themultilayer reflective film is formed, the multilayer reflective film isformed by ion beam sputtering by alternately irradiating a sputteringtarget of a high refractive index material and a sputtering target of alow refractive index material with an ion beam.

According to Configuration 8, as a result of forming a multilayerreflective film by a prescribed ion beam sputtering method in the stepfor forming a multilayer reflective film, a multilayer reflective filmcan be reliably obtained having favorable reflectance properties withrespect to EUV light.

(Configuration 9)

Configuration 9 of the present invention is the method of manufacturinga reflective mask blank described in Configuration 7 or Configuration 8,wherein, when the absorber film is formed, the absorber film is formedby reactive sputtering using a sputtering target of an absorber filmmaterial, the absorber film is formed so as to contain a componentcontained in the atmospheric gas during reactive sputtering, and theflow rate of the atmospheric gas is controlled so that the root meansquare roughness (Rms) is not more than 0.5 nm and the power spectrumdensity is not more than 50 nm⁴.

According to Configuration 9, an absorber film having a prescribedcomposition can be obtained by forming the absorber film by reactivesputtering in the step for forming the absorber film. As a result ofadjusting the flow rate of atmospheric gas when depositing by reactivesputtering, the root mean square roughness (Rms) of the surface of themask blank multilayer film containing the absorber film, and the powerspectrum density, which is the amplitude intensity of all roughnesscomponents detectable in a 3 μm×3 μm region at a spatial frequency of 1μm⁻¹ to 10 μm⁻¹, can be adjusted to be within a prescribed range ofvalues.

(Configuration 10)

Configuration 10 of the present invention is the method of manufacturinga reflective mask blank described in Configuration 9, wherein theatmospheric gas is a mixed gas containing an inert gas and nitrogen gas.

According to Configuration 10, an absorber film that has a suitablecomposition can be obtained, since the nitrogen flow rate can beadjusted as a result of the atmospheric gas during formation of theabsorber film by reactive sputtering being a mixed gas containing aninert gas and nitrogen. As a result thereof, an absorber film can bereliably obtained that has a suitable root mean square roughness (Rms)and power spectrum density on the surface of a mask blank multilayerfilm.

(Configuration 11)

Configuration 11 of the present invention is the method of manufacturinga reflective mask blank described in any of Configurations 7 to 10,wherein the absorber film is formed using a sputtering target of amaterial containing tantalum.

According to Configuration 11, as a result of forming the absorber filmusing a sputtering target of a material containing tantalum when formingthe absorber film by reactive sputtering, an absorber film can be formedthat contains tantalum and has suitable absorption. In addition, anabsorber film having a suitable root mean square roughness (Rms) andpower spectrum density on the surface of a mask blank multilayer filmcan be more reliably obtained.

(Configuration 12)

Configuration 12 of the present invention is the method of manufacturinga reflective mask blank described in Configuration 7 or Configuration 8,wherein, when the absorber film is formed, the absorber film is formedby sputtering using a sputtering target of a material of the absorberfilm, and the material and film thickness of the absorber film areselected so that the surface of the absorber film has a root mean squareroughness (Rms) of not more than 0.5 nm and a power spectrum density ata spatial frequency of 1 μm⁻¹ to 10 μm⁻¹ of not more than 50 nm⁴.

According to Configuration 12, as a result of selecting the material andfilm thickness of the absorber film in the step for forming an absorberfilm, the root mean square roughness (Rms) of the surface of a maskblank multilayer film containing the absorber film, and the powerspectrum density, which is the amplitude intensity of all roughnesscomponents detectable in a 3 μm×3 μm region at a spatial frequency of 1μm⁻¹ to 10 μm⁻¹, can be adjusted so as to be within a prescribed rangeof values.

(Configuration 13)

Configuration 13 of the present invention is the method of manufacturinga reflective mask blank described in Configuration 12, wherein thematerial of the absorber film is a material that contains nitrogen, andthe film thickness of the absorber film is not more than 60 nm.

According to Configuration 13, as a result of the material of theabsorber film containing nitrogen and the film thickness of the absorberfilm being not more than 60 nm, in addition to being able to reduceshadowing effects, the root mean square roughness (Rms) of the surfaceof the absorber film and the power spectrum density, which is theamplitude intensity of all roughness components detectable in a 3 μm×3μm region at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹, can be furtherreduced, and a reflective mask blank is obtained, the reflective maskblank being capable of inhibiting the detection of pseudo defects in adefect inspection using a highly sensitive defect inspection apparatus.

(Configuration 14)

Configuration 14 of the present invention is the method of manufacturinga reflective mask blank described in any of Configurations 7 to 13,further comprising forming a protective film arranged in contact withthe surface of the multilayer reflective film.

According to Configuration 14, since damage to the surface of themultilayer reflective film can be inhibited when fabricating a transfermask (EUV mask) as a result of further comprising a step for forming aprotective film, reflectance properties with respect to EUV light can befurther improved. In addition, in the resulting reflective mask blank,detection of pseudo defects in a defect inspection of the surface of theprotective film using a highly sensitive defect inspection apparatus canbe inhibited, and critical defects can be made to be more conspicuous.

(Configuration 15)

Configuration 15 of the present invention is the method of manufacturinga reflective mask blank described in Configuration 14, wherein theprotective film is formed by ion beam sputtering by irradiating asputtering target of a protective film material with an ion beam.

According to Configuration 15, since smoothing of the surface of theprotective film is obtained by forming the protective film by ion beamsputtering using a sputtering target of a protective film material inthe step for forming the absorber film, the absorber film formed on theprotective film and the surface of an etching mask formed on theabsorber film can be smoothened, thereby making this preferable.

(Configuration 16)

Configuration 16 of the present invention is the method of manufacturinga reflective mask blank described in any of Configurations 7 to 15,further comprising forming an etching mask film arranged in contact withthe surface of the absorber film.

According to Configuration 16, as a result of forming an etching maskfilm having different dry etching properties from those of the absorberfilm, a highly precise transfer pattern can be formed when forming atransfer pattern on the absorber film.

(Configuration 17)

Configuration 17 of the present invention is a reflective mask having anabsorber pattern, obtained by patterning the absorber film of thereflective mask blank described in any of Configurations 1 to 6 or areflective mask blank obtained according to the method of manufacturinga reflective mask blank described in any of Configurations 7 to 16, onthe multilayer reflective film.

According to the reflective mask of Configuration 17, detection ofpseudo defects in a defect inspection using a highly sensitive defectinspection apparatus can be inhibited, and critical defects can be madeto be more conspicuous.

(Configuration 18)

Configuration 18 of the present invention is a method of manufacturing asemiconductor device, comprising: a step for forming a transfer patternon a transferred substrate by carrying out a lithography process with anexposure apparatus using the reflective mask described in Configuration17.

According to the method of manufacturing a semiconductor device ofConfiguration 18, since a reflective mask from which contaminants,scratches and other critical defects have been removed can be used in adefect inspection using a highly sensitive defect inspection apparatus,a circuit pattern or other transfer pattern transferred to a resist filmformed on a transferred substrate such as a semiconductor substrate isfree of defects, and a semiconductor device that has a fine and highlyprecise transfer pattern can be fabricated.

Effects of the Invention

According to the reflective mask blank and reflective mask of thepresent invention as previously described, the discovery ofcontaminants, scratches or other critical defects can be facilitated byinhibiting detection of pseudo defects attributable to surface roughnessof a substrate or film in a defect inspection using a highly sensitivedefect inspection apparatus. In a reflective mask blank and reflectivemask used in EUV lithography in particular, a multilayer reflective filmformed on a main surface of a substrate, which exhibits highreflectance, is obtained while inhibiting pseudo defects. In addition,the aforementioned reflective mask blank can be reliably fabricatedaccording to the method of manufacturing a reflective mask blank of thepresent invention as previously described.

In addition, according to the method of manufacturing a semiconductordevice as previously described, since a reflective mask from whichcontaminants, scratches and other critical defects have been removed canbe used in a defect inspection using a highly sensitive defectinspection apparatus, a circuit pattern or other transfer pattern formedon a transferred substrate such as a semiconductor substrate is free ofdefects, and a semiconductor device can be fabricated that has a fineand highly precise transfer pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a perspective view showing a mask blank substrate accordingto one embodiment of the present invention.

FIG. 1(b) is a cross-sectional schematic diagram showing a mask blanksubstrate of the present embodiment.

FIG. 2 is a cross-sectional schematic diagram showing one example of theconfiguration of a substrate with a multilayer reflective film accordingto one embodiment of the present invention.

FIG. 3 is a cross-sectional schematic diagram showing one example of theconfiguration of a reflective mask blank according to one embodiment ofthe present invention.

FIG. 4 is a cross-sectional schematic diagram showing one example of areflective mask according to one embodiment of the present invention.

FIG. 5 is a cross-sectional schematic diagram showing another example ofthe configuration of a reflective mask blank according to one embodimentof the present invention.

FIG. 6 is a graph indicating the results of analyzing the power spectraof the surfaces of absorber films of reflective mask blanks of anExample Sample 1 and Comparative Example Sample 1 of the presentinvention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The present invention is a reflective mask blank having a mask blankmultilayer film comprising a multilayer reflective film, obtained byalternately laminating a high refractive index layer and a lowrefractive index layer, and an absorber film on a main surface of a maskblank substrate.

FIG. 5 is a schematic diagram showing one example of a reflective maskblank 30 of the present invention. The reflective mask blank 30 of thepresent invention has a mask blank multilayer film 26 on a main surfaceof a mask blank substrate 10. In the present description, the mask blankmultilayer film 26 refers to a plurality of films, comprising amultilayer reflective film 21 and an absorber film 24, formed bylaminating on a main surface of the mask blank substrate 10. The maskblank multilayer film 26 can further comprise a protective film 22formed between the multilayer reflective film 21 and the absorber film24, and/or an etching mask film 25 formed on the surface of the absorberfilm 24. In the case of the reflective mask blank 30 shown in FIG. 5,the mask blank multilayer film 26 on a main surface of the mask blanksubstrate 10 has the multilayer reflective film 21, the protective film22, the absorber film 24 and the etching mask film 25. Furthermore, insubsequent explanations, with respect to the etching mask film 25, theetching mask film 25 is assumed to be stripped after having formed atransfer pattern on the absorber film 24. However, in the reflectivemask blank 30 in which the etching mask film 25 is not formed, alaminated structure having a plurality of layers is employed for theabsorber film 24, and the reflective mask blank 30 may be that in whichthe absorber film 24 has been given the function of an etching mask byusing materials having mutually different etching properties for thematerials composing the plurality of layers.

In the present description, “having a mask blank multilayer film 26 on amain surface of the mask blank substrate 10” refers to the case in whichthe mask blank multilayer film 26 is arranged in contact with thesurface of the mask blank substrate 10, as well as the case in whichanother film is present between the mask blank substrate 10 and the maskblank multilayer film 26. In addition, “a film A arranged in contactwith the surface of a film B” refers to film A and film B being arrangedso as to make direct contact without having another film interposedbetween film A and film B.

FIG. 3 is a schematic diagram showing another example of the reflectivemask blank 30 of the present invention. In the case of the reflectivemask blank 30 of FIG. 3, although the mask blank multilayer film 26 hasthe multilayer reflective film 21, the protective film 22 and theabsorber film 24, it does not have the etching mask film 25.

The reflective mask blank 30 of the present invention has a root meansquare roughness (Rms), obtained by measuring a 3 μm×3 μm region on thesurface of the reflective mask blank 30 where the mask blank multilayerfilm 26 is formed with an atomic force microscope, of not more than 0.5nm and a power spectrum density at a spatial frequency of 1 μm⁻¹ to 10μm⁻¹ of not more than 50 nm⁴.

According to the reflective mask blank 30 of the present invention, thediscovery of contaminants, scratches or other critical defects can befacilitated by inhibiting the detection of pseudo defects attributableto surface roughness of a substrate or film in a defect inspection usinga highly sensitive defective inspection apparatus.

Next, the following provides an explanation of the parameters of surfaceroughness (Rmax, Rms) and power spectrum density (PSD), which indicatethe surface morphology of a main surface of the reflective mask blank 30on which the mask blank multilayer film 26 is formed.

First, Rms (root mean square), which is a typical indicator of surfaceroughness, refers to root mean square roughness and is the square rootof the value obtained by averaging the squares of the deviation from anaverage line to a measurement curve. Rms is represented by the followingformula (1):

$\begin{matrix}\lbrack {{Equation}\mspace{14mu} 1} \rbrack & \; \\{{R\; m\; s} = \sqrt{\frac{1}{l}{\int_{0}^{1}{{Z^{2}\ (x)}{\mathbb{d}x}}}}} & (1)\end{matrix}$wherein, l represents a reference length and Z represents the heightfrom the average line to the measurement curve.

Similarly, Rmax, which is also a typical indicator of surface roughness,is the maximum height of surface roughness, and is the differencebetween the absolute values of maximum peak height and maximum troughdepth on a roughness curve (difference between the highest peak and thedeepest trough).

Rms and Rmax have conventionally been used to manage the surfaceroughness of the mask blank substrate 10, and are superior with respectto enabling surface roughness to be ascertained in terms of numericalvalues. However, since Rms and Rmax both only consist of informationrelating to height, they do not contain information relating to subtlechanges in surface morphology.

In contrast, power spectrum analysis, which represents surface roughnessusing amplitude intensity at a spatial frequency by converting surfaceirregularities of the resulting surface to spatial frequency regions,enables quantification of subtle changes in surface morphology. WhenZ(x,y) is taken to represent height data at an x coordinate and ycoordinate, then the Fourier transformation thereof is given by thefollowing equation (2).

$\begin{matrix}\lbrack {{Equation}\mspace{14mu} 2} \rbrack & \; \\{{F( {u,v} )} = {\frac{1}{N_{x}N_{y}}{\sum\limits_{u = 0}^{N_{x} - 1}\;{\sum\limits_{v = 0}^{N_{y} - 1}\;{{Z( {x,y} )}{\exp\lbrack {{- {\mathbb{i}}}\; 2{\pi( {\frac{u\; x}{N_{x}} + \frac{v\; y}{N_{y}}} )}} \rbrack}}}}}} & (2)\end{matrix}$

Here, N_(x) and N_(y) represent the number of data sets in the xdirection and y direction, u represents 0, 1, 2, . . . Nx−1, vrepresents 0, 1, 2 . . . Ny−1, and spatial frequency f at this time isgiven by the following equation (3).

$\begin{matrix}\lbrack {{Equation}\mspace{14mu} 3} \rbrack & \; \\{f = \{ {\lbrack \frac{u}{( {N_{x} - 1} )d_{x}} \rbrack^{2} + \lbrack \frac{v}{( {N_{y} - 1} )d_{y}} \rbrack^{2}} \}^{1/2}} & (3)\end{matrix}$

Here, in equation (3), d_(x) represents the minimum resolution in the xdirection while d_(y) represents the minimum resolution in the ydirection.

Power spectrum density PSD at this time is given by the followingequation (4).[Equation 4]P(u,v)=|F(u,v)|²  (4)

This power spectrum analysis is superior in that it not only makes itpossible to ascertain changes in the surface morphology of the maskblank multilayer film 26 of the reflective mask blank 30 as simplechanges in height, but also as changes at that spatial frequency, andenables analysis of the effects of microscopic reactions at the atomiclevel on the surface.

In the reflective mask blank 30 of the present invention, in order toobtain the aforementioned object, the root mean square roughness (Rms)of the surface of the mask blank multilayer film 26, obtained bymeasuring a 3 μm×3 μm region with an atomic force microscope, is notmore than 0.5 nm, and power spectrum density at a spatial frequency of 1μm⁻¹ to 10 μm⁻¹ is not more than 50 nm⁴, using the surface roughness(Rms) and power spectrum density described above.

In the present invention, the aforementioned 3 μm×3 μm region may be anyarbitrary location of a region where a transfer pattern is formed. Inthe case the mask blank substrate 10 is a 6025 size (152 mm×152 mm×6.35mm), then the transfer pattern formation region can be, for example, a142 mm×142 mm region, obtained by excluding the peripheral region of thesurface of the reflective mask blank substrate 30, a 132 mm×132 mmregion or a 132 mm×104 mm region. In addition, the aforementionedarbitrary location can be a region located in the center of the surfaceof the reflective mask blank 30, for example.

In addition, in the present invention, the aforementioned 3 μm×3 μmregion can be a region located in the center of the film surface of themask blank laminated film 26. For example, in the case the film surfaceof the mask blank laminated film 26 of the reflective mask blank 30 hasa rectangular shape, the aforementioned center is located at theintersection of the diagonal lines of the aforementioned rectangle.Namely, the aforementioned intersection and the center of theaforementioned region (and the center of the region is the same as thecenter of the film surface) coincide.

In addition, the previously explained 3 μm×3 μm region, the transferpattern formation region and the arbitrary location can also be appliedto the mask blank substrate 10 and a substrate with a multilayerreflective film 20 depending on the case.

In addition, in the case of carrying out a defect inspection on thesurface of the reflective mask blank 30 using a highly sensitive defectinspection apparatus using inspection light in a wavelength region of150 nm to 365 nm, such as a highly sensitive defect inspection apparatususing a UV laser having an inspection light source frequency of 266 nmor an ArF excimer laser having an inspection light source frequency of193 nm, the power spectrum density at a spatial frequency of 1 μm⁻¹ to10 μm⁻¹ obtained by measuring a 3 μm×3 μm region of the aforementionedsurface with an atomic force microscope can be made to be not more than50 nm⁴, the power spectrum density at a spatial frequency of 1 μm⁻¹ to10 μm⁻¹ is preferably not more than 45 nm⁴, the power spectrum densityat a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹ is more preferably not morethan 40 nm⁴, the power spectrum density at a spatial frequency of 1 μm⁻¹to 10 μm⁻¹ is even more preferably not more than 35 nm⁴, and the powerspectrum density at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹ is stillmore preferably not more than 30 nm⁴.

In addition, the aforementioned root mean square roughness (Rms) ispreferably not more than 0.5 nm, more preferably not more than 0.45 nm,even more preferably not more than 0.40 nm, even more preferably notmore than 0.35 nm, even more preferably not more than 0.30 nm, and stillmore preferably not more than 0.25 nm. In addition, maximum height(Rmax) is preferably not more than 5 nm, more preferably not more than4.5 nm, even more preferably not more than 4 nm, even more preferablynot more than 3.5 nm, even more preferably not more than 3 nm, and stillmore preferably not more than 2.5 nm.

In addition, in the reflective mask blank 30 of the present invention,in order to achieve the aforementioned object, an integrated value I ofthe power spectrum density at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹obtained by measuring a 3 μm×3 μm region of the surface of the maskblank multilayer film 26 with an atomic force microscope is preferablynot more than 800×10⁻³ nm³. The aforementioned integrated value I ismore preferably not more than 650×10⁻³ nm³. The aforementionedintegrated value I is even more preferably not less than 500×10⁻³ nm³.The aforementioned integrated value I is particularly preferably notmore than 450×10⁻³ nm³.

According to the reflective mask blank 30 of the present invention, thediscovery of contaminants, scratches or other critical defects can befacilitated by inhibiting detection of pseudo defects attributable tosurface roughness of a substrate or film in a defect inspection using ahighly sensitive defect inspection apparatus.

Next, a detailed explanation is provided of the reflective mask blank 30of the present invention.

[Mask Blank Substrate 10]

First, an explanation is provided of the mask blank substrate 10 thatcan be used to fabricate the reflective mask blank 30 of the presentinvention.

FIG. 1(a) is a perspective view showing one example of the mask blanksubstrate 10 that can be used to fabricate the reflective mask blank 30of the present invention. FIG. 1(b) is a cross-sectional schematicdiagram of the mask blank substrate 10 shown in FIG. 1(a).

The mask blank substrate 10 (which may be simply referred to as thesubstrate 10) is a rectangular plate-like body, and has two opposingmain surfaces 2 and an edge face 1. The two opposing main surfaces 2constitute an upper surface and a lower surface of this plate-like body,and are formed so as to be mutually opposing. In addition, at least oneof the two opposing main surfaces 2 is a main surface on which atransfer pattern is to be formed.

The edge face 1 constitutes the lateral surface of this plate-like body,and is adjacent to the outer edges of the opposing main surfaces 2. Theedge face 1 has a flat edge face portion 1 d and a curved edge faceportion 1 f. The flat edge face portion 1 d is a surface that connects aside of one of the opposing main surfaces 2 and a side of the otheropposing main surface 2, and comprises a lateral surface portion 1 a anda chamfered surface portion 1 b. The lateral surface portion 1 a is aportion (T surface) that is nearly perpendicular to the opposing mainsurfaces 2 in the flat edge face portion 1 d. The chamfered surfaceportion 1 b is a portion (C surface) that is chamfered between thelateral surface portion 1 a and the opposing main surfaces 2, and isformed between the lateral surface portion 1 a and the opposing mainsurfaces 2

The curved edge face portion 1 f is a portion (R portion) that isadjacent to the vicinity of a corner portion 10 a of the substrate 10when the substrate 10 is viewed from overhead, and comprises a lateralsurface portion 1 c and a chamfered surface portion 1 e. Here, when thesubstrate 10 is viewed from overhead, the substrate 10 appears in, forexample, a direction perpendicular to the opposing main surfaces 2. Inaddition, the corner portion 10 a of the substrate 10 refers to, forexample, the vicinity of the intersection of two sides along the outeredge of the opposing main surfaces 2. An intersection of two sides isthe intersection of lines respectively extending from two sides. In thepresent example, the curved end face portion if is formed into a curvedshape by rounding the corner portion 10 a of the substrate 10.

In order to more reliably achieve the object of the present invention,the main surfaces of the mask blank substrate 10 used in the reflectivemask blank 30 of the present invention and the surface of the multilayerreflective film 21 of the substrate with a multilayer reflective film 20preferably have a prescribed surface roughness and a prescribed powerspectrum density (PSD) in the same manner as the surface of thereflective mask blank 30 of the present invention.

In addition, the surface of the mask blank substrate 10 is preferablyprocessed by catalyst referred etching (CARE). CARE refers to a surfaceprocessing method involving arranging a processing target (mask blanksubstrate) and catalyst in a treatment liquid or supplying a treatmentliquid between the processing target and the catalyst, allowing theprocessing target and catalyst to make contact, and processing theprocessing target with an active species generated from molecules in thetreatment liquid that have been adsorbed on the catalyst at that time.Furthermore, in the case the processing target is composed of a solidoxide such as glass, water is used for the treatment liquid, theprocessing target and the catalyst are allowed to make contact in thepresence of the water, and the catalyst and surface of the processingtarget are allowed to undergo relative motion and the like to removedecomposition products of hydrolysis from the surface of the processingtarget.

Main surfaces of the mask blank substrate 10 are selectively processedby catalyst referred etching starting from protrusions that contact areference surface in the form of a catalyst surface. Consequently,surface irregularities (surface roughness) that compose the mainsurfaces retain an extremely high level of smoothness resulting in anextremely uniform surface morphology, while also resulting in a surfacemorphology in which the proportion of concave portions that compose thereference surface is greater than the proportion of convex portions.Thus, in the case of laminating a plurality of thin films on theaforementioned main surfaces, since the size of defects on the mainsurfaces tends to become small, surface processing by catalyst referredetching is preferable in terms of defect quality. This effect isespecially demonstrated in the case of forming the multilayer reflectivefilm 21 to be subsequently described on the aforementioned main surfacesin particular. In addition, as a result of processing the main surfacesby catalyst referred etching as previously described, a surface having aprescribed range of surface roughness and a prescribed power spectrumdensity as previously described can be formed comparatively easily.

Furthermore, in the case the material of the substrate 10 is a glassmaterial, at least one type of material selected from the groupconsisting of platinum, gold, transition metals and alloys comprising atleast one of these materials can be used for the catalyst. In addition,at least one type of liquid selected from the group consisting of purewater, functional water such as ozonated water or hydrogen water,low-concentration aqueous alkaline solutions and low-concentrationaqueous acidic solutions can be used for the treatment liquid.

As a result of making the surface roughness and power spectrum densityof a main surface to be within the aforementioned ranges as previouslydescribed, detection of pseudo defects can be significantly inhibited ina defect inspection by, for example, the “MAGICS M7360”Mask/Substrate/Blank Defect Inspection Apparatus for EUV Exposuremanufactured by Lasertec Corp. (inspection light source wavelength: 266nm) or the “Teron 610” Reticule, Optical Mask/Blank and UV Mask/BlankDefect Inspection Apparatuses manufactured by KLA-Tencor Corp.(inspection light source wavelength: 193 nm).

Furthermore, the aforementioned inspection light source wavelength isnot limited to 266 nm and 193 nm. A wavelength of 532 nm, 488 nm, 364 nmor 257 nm may also be used for the inspection light source wavelength.

A main surface on the side, on which a transfer pattern of the maskblank substrate 10 used in the reflective mask blank 30 of the presentinvention is formed, is preferably processed so as to have high flatnessat least from the viewpoints of obtaining pattern transfer accuracy andpositional accuracy. In the case of an EUV reflective mask blanksubstrate, flatness in a 132 mm×132 mm region or a 142 mm×142 mm regionon a main surface of the substrate 10 on the side on which a transferpattern is formed is preferably not more than 0.1 μm and particularlypreferably not more than 0.05 μm. In addition, flatness in a 132 mm×132mm region on a main surface of the substrate 10 on which a transferpattern is formed is more preferably not more than 0.03 μm. In addition,the main surface on the opposite side from the side on which a transferpattern is formed is the side that is clamped with an electrostaticchuck when the substrate is placed in an exposure apparatus, andflatness in a 142 mm×142 mm region is preferably not more than 1 μm andparticularly preferably not more than 0.5 μm.

Any material may be used for the material of the reflective mask blanksubstrate 10 for EUV exposure provided it has low thermal expansionproperties. For example, an SiO₂—TiO₂-based glass having low thermalexpansion properties (such as a two-element system (SiO₂—TiO₂) orthree-element system (such as SiO₂—TiO₂—SnO₂)), or a so-calledmulticomponent glass such as SiO₂—Al₂O₃—Li₂O-based crystallized glass,can be used. In addition, a substrate other than the aforementionedglass made of silicon or metal and the like can also be used. An exampleof the aforementioned metal substrate is an invar alloy (Fe—Ni-basedalloy).

As was previously described, in the case of the mask blank substrate 10for EUV exposure, a multicomponent glass material is used since thesubstrate is required to have low thermal expansion properties. However,there is the problem of it being difficult to obtain high smoothnesswith a multicomponent glass material in comparison with synthetic quartzglass. In order to solve this problem, a thin film composed of a metalor an alloy, or a thin film composed of a material containing at leastone of oxygen, nitrogen and carbon in a metal or alloy, is formed on asubstrate composed of a multicomponent glass material. A surface havinga surface roughness and a power spectrum density within theaforementioned ranges can then be formed comparatively easily bysubjecting the surface of the thin film to mirror polishing and surfacetreatment.

Preferable examples of the material of the aforementioned thin filminclude Ta (tantalum), alloys containing Ta and Ta compounds containingat least one of oxygen, nitrogen and carbon in Ta or an alloy containingTa. Examples of Ta compounds that can be used include those selectedfrom TaB, TaN, TaO, TaON, TaCON, TaBN, TaBO, TaBON, TaBCON, TaHf, TaHfO,TaHfN, TaHfON, TaHfCON, TaSi, TaSiO, TaSiN, TaSiON and TaSiCON. Amongthese Ta compounds, TaN, TaON, TaCON, TaBN, TaBON, TaBCON, TaHfN,TaHfON, TaHfCON, TaSiN, TaSiON and TaSiCON that contain nitrogen (N) areused more preferably. Furthermore, from the viewpoint of high smoothnessof the thin film surface, the aforementioned thin film preferably has anamorphous structure. The crystal structure of the thin film can bemeasured with an X-ray diffraction (XRD) analyzer.

Furthermore, in the present invention, there are no particularlimitations on the processing method used to obtain surface roughnessand power spectrum density within the aforementioned defined ranges. Thepresent invention is characterized in the managing of the surfaceroughness and power spectrum density of the reflective mask blank 30,and can be realized by, for example, processing methods like thoseexemplified in the examples to be subsequently described.

[Substrate with Multilayer Reflective Film 20]

The following provides an explanation of the substrate with a multilayerreflective film 20 that can be used in the reflective mask blank 30 ofthe present invention.

FIG. 2 is a schematic diagram of one example of the substrate with amultilayer reflective film 20 able to be used in the reflective maskblank 30.

The substrate with a multilayer reflective film 20 of the presentembodiment has a structure having the multilayer reflective film 21 on amain surface of the previously explained mask blank substrate 10 on theside on which a transfer pattern is formed. This multilayer reflectivefilm 21 imparts a function of reflecting EUV light in a reflective mask40 for EUV lithography, and adopts a configuration in which elementshaving different refractive indices are cyclically laminated.

There are no particular limitations on the material of the multilayerreflective film 21 provided it reflects EUV light. The reflectance ofthe multilayer reflective film 21 alone is normally not less than 65%and the upper limit thereof is normally 73%. This type of multilayerreflective film 21 can be that of a multilayer reflective film 21 inwhich a thin film composed of a high refractive index material (highrefractive index layer) and a thin film composed of a low refractiveindex material (low refractive index layer) are alternately laminatedfor about 40 to 60 cycles.

For example, the multilayer reflective film 21 for EUV light of awavelength of 13 nm to 14 nm preferably consists of an Mo/Si cyclicallylaminated film obtained by alternately laminating about 40 cycles of anMo film and Si film. In addition, a multilayer reflective film used inthe region of EUV light can consist of, for example, an Ru/Si cyclicallylaminated film, Mo/Be cyclically laminated film, Mo compound/Si compoundcyclically laminated film, Si/Nb cyclically laminated film, Si/Mo/Rucyclically laminated film, Si/Mo/Ru/Mo cyclically laminated film orSi/Ru/Mo/Ru cyclically laminated film.

The method used to form the multilayer reflective film 21 is known inthe art. The multilayer reflective film 21 can be formed by depositingeach layer by, for example, magnetron sputtering or ion beam sputtering.In the case of the aforementioned Mo/Si cyclically laminated film, an Sifilm having a thickness of about several nm is first deposited on thesubstrate 10 using an Si target by, for example, ion beam sputtering,followed by depositing an Mo film having a thickness of about several nmusing an Mo target and, with this deposition comprising one cycle,laminating for 40 to 60 cycles, to form the multilayer reflective film21.

When fabricating the reflective mask blank 30 of the present invention,the multilayer reflective film 21 is preferably formed by ion beamsputtering by alternately irradiating a sputtering target of a highrefractive index material and a sputtering target of a low refractiveindex material. As a result of forming the multilayer reflective film bya prescribed ion beam sputtering method, the multilayer reflective film21 having favorable reflectance properties with respect to EUV light canbe reliably obtained.

In the reflective mask blank 30 of the present invention, the mask blankmultilayer film 26 preferably further comprises the protective film 22arranged in contact with the surface of the multilayer reflective film21 on the opposite side from the mask blank substrate 10.

The protective film 22 (see FIG. 3) can be formed to protect themultilayer reflective film 21 from dry etching or wet cleaning in themanufacturing process of the reflective mask 40 for EUV lithography. Inthis manner, an aspect having the multilayer reflective film 21 and theprotective film 22 on the mask blank substrate 10 can also constitutethe substrate with a multilayer reflective film 20 in the presentinvention.

Furthermore, materials selected from, for example, Ru, Ru—(Nb, Zr, Y, B,Ti, La, Mo), Si—(Ru, Rh, Cr, B), Si, Zr, Nb, La and B can be used forthe material of the aforementioned protective film 22. Among thesematerials, reflectance properties of the multilayer reflective film 21can be made more favorable if a material comprising ruthenium (Ru) isapplied. More specifically, the material of the protective film 22 ispreferably Ru or Ru—(Nb, Zr, Y, B, Ti, La, Mo). This type of protectivefilm 22 is particularly effective in the case of patterning the absorberfilm 24 using a Ta-based material for the absorber film and dry etchingusing a Cl-based gas.

Furthermore, in the aforementioned substrate with a multilayerreflective film 20, the surface of the multilayer reflective film 21 orthe protective film 22 is such that the power spectrum density at aspatial frequency of 1 μm⁻¹ to 10 μm⁻¹, obtained by measuring a 0.3mm×0.3 mm region thereof with an atomic force microscope, is not morethan 25 nm⁴, preferably not more than 22.5 nm⁴ and even more preferablynot more than 20 nm⁴. As a result of configuring in this manner, in thecase of carrying out a defect inspection on the substrate with amultilayer reflective film 20 with a highly sensitive defect inspectionapparatus that uses inspection light in the wavelength region of 150 nmto 365 nm, such as the previously mentioned highly sensitive inspectionapparatus using a UV laser having an inspection light source wavelengthof 266 nm or ArF excimer laser having an inspection light sourcewavelength of 193 nm, detection of pseudo defects can be inhibitedsignificantly while also enabling critical defects to be made moreconspicuous.

Moreover, in addition to the effect of enabling the detection of pseudodefects to be inhibited significantly in a defect inspection using ahighly sensitive defect inspection apparatus as previously described, inorder to improve reflection properties required for use as the substratewith a multilayer reflective film 20, the root mean square roughness(Rms) of the aforementioned substrate with a multilayer reflective film20 on the surface of the multilayer reflective film 21 or the protectivefilm 22 obtained by measuring a 3 μm×3 μm region with an atomic forcemicroscope is not more than 0.25 nm, preferably not more than 0.20 nmand more preferably not more than 0.15 nm.

In order to maintain the surface morphology of the aforementionedsubstrate 10 within the aforementioned ranges and allow the surface ofthe multilayer reflective film 21 or the protective film 22 to have apower spectrum density within the aforementioned ranges, the multilayerreflective film 21 is obtained by depositing by sputtering so that ahigh refractive index layer and a low refractive index layer accumulateon an angle to the normal of a main surface of the substrate 10. Morespecifically, the incident angle of sputtered particles for depositing alow refractive index layer consisting of Mo and the like and theincident angle of sputtered particles for depositing a high refractiveindex layer consisting of Si and the like are greater than 0 degrees tonot more than 45 degrees, more preferably greater than 0 degrees to notmore than 40 degrees, and even more preferably greater than 0 degrees tonot more than 30 degrees. Moreover, the protective film 22 formed on themultilayer reflective film 21 is also preferably formed by ion beamsputtering in continuation therefrom so that the protective film 22accumulates on an angle to the normal of a main surface of the substrate10.

In addition, in the substrate with a multilayer reflective film 20, aback side electrically conductive film 23 (see FIG. 3) for the purposeof electrostatic clamping can also be formed on the surface of the maskblank substrate 10 on the opposite side from the surface contacting themultilayer reflective film 21 of the substrate 10. In this manner, anaspect having the multilayer reflective film 21 and the protective film22 on the side of the mask blank substrate 10 on which a transferpattern is formed, and having the back side electrically conductive film23 on the surface on the opposite side from the surface contacting themultilayer reflective film 21, also constitutes the substrate with amultilayer reflective film 20 in the present invention. Furthermore, theelectrical property (sheet resistance) required by the back sideelectrically conductive film 23 is normally not more than 100 Ω/square.The method used to form the back side electrically conductive film 23 isa known method, and it can be formed, for example, using a metal oralloy target of Cr or Ta and the like by magnetron sputtering or ionbeam sputtering.

In addition, the substrate with a multilayer reflective film 20 of thepresent embodiment may also have a base layer formed between the maskblank substrate 10 and the multilayer reflective film 21. The base layercan be formed for the purpose of improving smoothness of a main surfaceof the substrate 10, reducing defects, demonstrating the effect ofenhancing reflectance of the multilayer reflective film 21, andcompensating for stress in the multilayer reflective film 21.

[Reflective Mask Blank 30]

The following provides an explanation of the reflective mask blank 30 ofthe present invention.

FIG. 3 is a schematic diagram showing one example of the reflective maskblank 30 of the present invention.

The reflective mask blank 30 of the present invention employs aconfiguration in which an absorber film 24 serving as a transfer patternis formed on the protective film 22 of the substrate with a multilayerreflective film 20 that is previously explained.

The aforementioned absorber film 24 is only required to be that whichhas a function that absorbs exposure light in the form of EUV light, andhas a desired difference in reflectance between light reflected by theaforementioned multilayer reflective film 21 and the protective film 22and light reflected by an absorber pattern 27.

For example, reflectance with respect to EUV light of the absorber film24 is set to between 0.1% and 40%. Moreover, in addition to theaforementioned difference in reflectance, the absorber film 24 may alsohave a desired phase difference between light reflected by theaforementioned multilayer reflective film 21 or the protective film 22,and light reflected by the absorber pattern 27. Furthermore, in the caseof having such a phase difference between reflected light, the absorberfilm 24 in the reflective mask blank 30 may be referred to as a phaseshift film. In the case of improving the contrast of reflected light ofa reflective mask obtained by providing the aforementioned desired phasedifference between reflected light, the phase difference is preferablyset to within the range of 80 degrees±10 degrees, the reflectance of theabsorber film 24 in terms of absolute reflectance is preferably set to1.5% to 30%, and the reflectance of the absorber film 24 with respect tothe surface of the multilayer reflective film 21 and/or the protectivefilm 22 is preferably set to 2% to 40%.

The aforementioned absorber film 24 may be a single layer or amultilayered structure. In the case of a multilayered structure, thelaminated films may be of the same material or different materials. Thelaminated film can be that in which the materials and composition changeincrementally and/or continuously in the direction of film thickness.

There are no particular limitations on the material of theaforementioned absorber film 24. For example, a material having thefunction of absorbing EUV light that is composed of Ta (tantalum) aloneor a material having Ta as the main component thereof is usedpreferably. A material having Ta as the main component thereof isnormally a Ta alloy. The crystalline state of this absorber film 24 issuch that it preferably has an amorphous or microcrystalline structurefrom the viewpoints of smoothness and flatness. Examples of materialsthat can be used for the material having Ta as the main componentthereof include materials selected from materials containing Ta and B,materials containing Ta and N, materials containing Ta and B and furthercontaining at least O or N, materials containing Ta and Si, materialscontaining Ta, Si and N, materials containing Ta and Ge, and materialscontaining Ta, Ge and N. In addition, an amorphous structure is easilyobtained by adding, for example, B, Si or Ge and the like to Ta, therebymaking it possible to improve smoothness. Moreover, if N and/or O areadded to Ta, resistance to oxidation improves, thereby making itpossible to improve stability over time. In order to maintain thesurface morphology of the substrate 10 and the substrate with amultilayer reflective film 20 within the aforementioned ranges and allowthe surface of the absorber film 24 to have a power spectrum densitywithin the aforementioned ranges, a microcrystalline structure oramorphous structure is preferably employed for the absorber film 24.Crystal structure can be confirmed with an X-ray diffraction (XRD)instrument.

More specifically, examples of materials containing tantalum that formthe absorber film 24 include tantalum metal and materials that containtantalum and one or more elements selected from nitrogen, oxygen, boronand carbon, but do not substantially contain hydrogen. Examples thereofinclude Ta, TaN, TaON, TaBN, TaBON, TaCN, TaCON, TaBCN and TaBOCN. Theaforementioned materials may also contain metals other than tantalumwithin a range that allows the effects of the present invention to beobtained. When the material, containing tantalum that forms the absorberfilm 24, contains boron, it facilitates to control the absorber film 24so as to adopt an amorphous (non-crystalline) structure.

The absorber film 24 of the mask blank is preferably formed with amaterial containing tantalum and nitrogen. The nitrogen content in theabsorber film 24 is preferably not more than 50 at %, more preferablynot more than 30 at %, even more preferably not more than 25 at % andstill more preferably not more than 20 at %. The nitrogen content in theabsorber film 24 is preferably not less than 5 at %.

In the reflective mask blank 30 of the present invention, the absorberfilm 24 preferably contains tantalum and nitrogen and the nitrogencontent is 10 at % to 50 at %, more preferably 15 at % to 50 at %, andeven more preferably 30 at % to 50 at %. As a result of the absorberfilm 24 containing tantalum and nitrogen and the nitrogen content being10 at % to 50 at %, the root mean square roughness (Rms) and the powerspectrum density, which is the amplitude intensity of all roughnesscomponents detectable in a 3 μm×3 μm region at a spatial frequency of 1μm⁻¹ to 10 μm⁻¹, on the surface of the absorber film 24 can be made tobe within the prescribed ranges of values, and since enlargement ofcrystal grains that compose the absorber film can be inhibited, patternedge roughness when patterning the absorber film can be reduced.

In the reflective mask blank 30 of the present invention, the filmthickness of the absorber film 24 is set to the film thickness requiredfor the absorber film 24 to have a desired difference in reflectancebetween light reflected by the multilayer reflective film 21 and theprotective film 22 and light reflected by the absorber pattern 27. Thefilm thickness of the absorber film 24 is preferably not more than 60 nmin order to reduce shadowing effects. As a result of making the filmthickness of the absorber film 24 to be 60 nm, the root mean squareroughness (Rms) and the power spectrum density, which is the amplitudeintensity of all roughness components detectable in a 3 μm×3 μm regionat a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹, of the surface of theabsorber film 24 can be further reduced, thereby making it possible toinhibit the detection of pseudo defects in a defect inspection using ahighly sensitive defect inspection apparatus.

In addition, in the reflective mask blank 30 of the present invention,the aforementioned absorber film 24 can be given a phase shift functionhaving a desired phase shift difference between light reflected by theaforementioned multilayer reflective film 21 and the protective film 22and light reflected by the absorber pattern 27. In that case, areflective mask blank that serves as the master of a reflective maskhaving improved transfer resolution by EUV light, is obtained. Inaddition, since the film thickness of the absorber required todemonstrate a phase shift effect needed to demonstrate desired transferresolution can be reduced in comparison with that in the prior art, areflective mask blank is obtained in which shadowing effects arereduced.

There are no particular limitations on the material of the absorber film24 having a phase shift function. For example, Ta alone or a materialhaving Ta as the main component thereof can be used as previouslydescribed, or another material may be used. Examples of materials otherthan Ta include Ti, Cr, Nb, Mo, Ru, Rh and W. In addition, an alloycontaining two or more elements among Ta, Ti, Cr, Nb, Mo, Ru, Rh and Wcan be used for the material, and a multilayer film can be usedconsisting of layers having these elements as materials thereof. Inaddition, one or more elements selected from nitrogen, oxygen and carbonmay also be contained in these materials. Among these, by employing amaterial containing nitrogen, the root mean square roughness (Rms) andthe power spectrum density, which is the amplitude intensity of allroughness components detectable in a 3 μm×3 μm region at a spatialfrequency of 1 μm⁻¹ to 10 μm⁻¹, of the surface of the absorber film canbe reduced, and a reflective mask blank that is able to inhibit thedetection of pseudo defects in a defect inspection using a highlysensitive defect inspection apparatus can be obtained, thereby makingthis preferable. Furthermore, in the case of using the absorber film 24in the form of a laminated film, the laminated film may be a laminatedfilm consisting of layers of the same material or a laminated filmconsisting of layers of different materials. In the case of using alaminated film consisting of layers of different materials for theabsorber film 24, the materials that compose this plurality of layersmay be materials having mutually different etching properties to obtainan absorber film 24 having an etching mask function.

In the case the uppermost surface of the reflective mask blank 30 of thepresent invention is the absorber film 24, the root mean squareroughness (Rms) and power spectrum density at a spatial frequency of 1μm⁻¹ to 10 μm⁻¹ in a 3 μm×3 μm region on the surface of the absorberfilm 24 are made to be within the prescribed ranges of values. Accordingto the reflective mask blank 30 of the present invention having such aconfiguration, the detection of pseudo defects attributable to surfaceroughness of a substrate or film in a defect inspection using a highlysensitive defect inspection apparatus can be inhibited, and thediscovery of contaminants or scratches and other critical defects can befacilitated.

Furthermore, the reflective mask blank 30 of the present invention isnot limited to the configuration shown in FIG. 3. For example, a resistfilm serving as a mask for patterning the aforementioned absorber film24 can also be formed on the absorber film 24, and this reflective maskwith a resist film 30 can also constitute the reflective mask blank 30of the present invention. Furthermore, the resist film formed on theabsorber film 24 may be a positive resist or negative resist. Inaddition, the resist film may also be for electron beam drawing or laserdrawing. Moreover, a so-called hard mask (etching mask) film can also beformed between the absorber film 24 and the aforementioned resist film,and this aspect can also constitute the reflective mask blank 30 of thepresent invention.

In the reflective mask blank 30 of the present invention, the mask blankmultilayer film 26 preferably further comprises the etching mask film 25arranged in contact with the surface of the absorber film 24 on theopposite side form the mask blank substrate 10. In the case of thereflective mask blank 30 shown in FIG. 5, the mask blank multilayer film26 on a main surface of the mask blank substrate 10 further has theetching mask film 25 in addition to the multilayer reflective film 21,the protective film 22 and the absorber film 24. The reflective maskblank 30 of the present invention may further have a resist film on theuppermost surface of the mask blank multilayer film 26 of the reflectivemask blank 30 shown in FIG. 5.

More specifically, in the reflective mask blank 30 of the presentinvention, in the case the material of the absorber film 24 uses Taalone or a material having Ta has the main component thereof, astructure is preferably employed in which the etching mask film 25composed of a material containing chromium is formed on the absorberfilm 24. As a result of employing the reflective mask blank 30 havingsuch a structure, the reflective mask 40 can be fabricated in whichoptical properties of the absorber film 24 with pattern are favorableeven if the etching mask film 25 is removed by dry etching using a mixedgas of a chlorine-based gas and oxygen gas after forming a transferpattern on the absorber film 24. In addition, a reflective mask 40 canbe fabricated in which line edge roughness of a transfer pattern formedon the absorber film 24 is favorable.

Examples of materials containing chromium that form the etching maskfilm 25 include materials containing chromium and one or more elementsselected from nitrogen, oxygen, carbon and boron. Examples thereofinclude CrN, CrON, CrCN, CrCON, CrBN, CrBON, CrBCN and CrBOCN. Theaforementioned materials may also contain materials other than chromiumwithin a range that allows the effects of the present invention to beobtained. The film thickness of the etching mask film 25 is preferablynot less than 3 nm from the viewpoints of functioning as an etching maskwith which a transfer pattern is accurately formed on the absorber film24. In addition, the film thickness of the etching mask film 25 ispreferably not more than 15 nm from the viewpoint of reducing filmthickness of the resist film.

In the case the uppermost surface of the reflective mask blank 30 of thepresent invention is the etching mask film 25, similar to the case ofthe uppermost surface of the reflective mask blank 30 being the absorberfilm 24, the root mean square roughness (Rms), obtained by measuring a 3μm×3 μm region on the surface of the etching mask film 25 with an atomicforce microscope, and the power spectrum density at a spatial frequencyof 1 μm⁻¹ to 10 μm⁻¹, can be made to be within the prescribed ranges ofvalues. According to the reflective mask blank 30 of the presentinvention having such a configuration, the detection of pseudo defectsattributable to surface roughness of a substrate or film in a defectinspection using a highly sensitive defect inspection apparatus can beinhibited, and the discovery of contaminants or scratches and othercritical defects can be facilitated.

The following provides an explanation of a method of manufacturing thereflective mask blank 30 of the present invention.

The present invention is a method of manufacturing the reflective maskblank 30 having the mask blank multilayer film 26, comprising themultilayer reflective film 21, obtained by mutually laminating a highrefractive index layer and a low refractive index layer, and theabsorber film 24, on a main surface of the mask blank substrate 10. Themethod of manufacturing the reflective mask blank 30 of the presentinvention comprises a step for forming the multilayer reflective film 21on a main surface of the mask blank substrate 10, and a step for formingthe absorber film 24 on the multilayer reflective film 21. In the methodof manufacturing the reflective mask blank 30 of the present invention,the absorber film 24 is formed so that the surface of the reflectivemask blank 30 has a root mean square roughness (Rms), obtained bymeasuring a 3 μm×3 μm region with an atomic force microscope, of notmore than 0.5 nm, and has a power spectrum density at a spatialfrequency of 1 μm⁻¹ to 10 μm⁻¹ of not more than 50 nm⁴.

On the surface of the reflective mask blank 30 of the present invention,by making Rms to not be more than 0.5 nm (preferably not more than 0.45nm, more preferably not more than 0.40 nm, and even more preferably notmore than 0.35 nm), and making the power spectrum density, which is theamplitude intensity of all roughness components detectable in a 3 μm×3μm region at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹, to not be morethan 50 nm⁴ (preferably not more than 45 nm⁴, more preferably not morethan 40 nm⁴ and even more preferably not more than 35 nm⁴), thereflective mask blank 30 can be fabricated in which the detection ofpseudo defects in a defect inspection using a highly sensitive defectinspection apparatus can be inhibited, and critical defects can be mademore conspicuous.

In the method of manufacturing the reflective mask blank 30 of thepresent invention, in the step for forming the absorber film 24, theabsorber film 24 is formed by reactive sputtering using a sputteringtarget composed of a material contained in the absorber film 24, and theabsorber film 24 is preferably formed so that a component contained inthe atmospheric gas during reactive sputtering is contained therein. Theroot mean square roughness (Rms) and the power spectrum density, whichis the amplitude intensity of all roughness components detectable in a 3μm×3 μm region at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹, of thesurface of the mask blank multilayer film 26 can be adjusted so as to bewithin the ranges of prescribed values by adjusting the flow rate ofatmospheric gas during deposition by reactive sputtering.

In the case of forming the absorber film 24 by reactive sputtering, theatmospheric gas is preferably a mixed gas containing an inert gas andnitrogen gas. In this case, since the flow rate of nitrogen can beadjusted, the absorber film 24 can be obtained having a suitablecomposition. As a result, the absorber film 24 having a suitable rootmean square roughness (Rms) and power spectrum density can be reliablyobtained on the surface of the mask blank multilayer film 26.

In the method of manufacturing the reflective mask blank 30 of thepresent invention, the absorber film 24 is preferably formed using asputtering target of a material containing tantalum. As a result, theabsorber film 24 that contains tantalum and has suitable absorption ofexposure light can be obtained.

In the method of manufacturing the reflective mask blank 30 of thepresent invention, in the step for forming the absorber film 24, theabsorber film 24 is formed by sputtering using a sputtering target of anabsorber film material, and materials and composition are selected sothat the surface of the absorber film 24 has a root mean squareroughness (Rms) of not more than 0.5 nm and a power spectrum density ofnot more than 50 nm⁴. The material of the aforementioned absorber film24 is selected from the previously exemplified materials, and the filmthickness of the absorber film 24 is set to a film thickness required tohave a desired reflectance difference between light reflected by themultilayer reflective film 21 and the protective film 22 and lightreflected by the absorber pattern 27. The film thickness of the absorberfilm 24 is preferably set to a range of not more than 60 nm.

The method of manufacturing the reflective mask blank 30 of the presentinvention preferably further comprises a step for forming the protectivefilm 22 arranged in contact with the surface of the multilayerreflective film 21. Since damage to the surface of the multilayerreflective film 21 can be inhibited when fabricating a transfer mask(EUV mask) by forming the protective film 22, reflectance propertieswith respect to EUV light can be further improved. In addition, in themanufactured reflective mask blank 30, detection of pseudo defects onthe surface of the protective film 22 in a defect inspection using ahighly sensitive defect inspection apparatus can be inhibited, therebymaking it possible to make critical defects more conspicuous.

The protective film 22 is preferably formed by ion beam sputtering inwhich a sputtering target of the material of the protective film 22 isirradiated with an ion beam. Since smoothing of the protective filmsurface is obtained by ion beam sputtering, the surface of the absorberfilm formed on the protective film and an etching mask film furtherformed on the absorber film can be smoothened.

The method of manufacturing the reflective mask blank 30 of the presentinvention preferably further comprises a step for forming the etchingmask 25 arranged in contact with the surface of the absorber film 24. Byforming the etching mask film 25 to have different dry etchingproperties than those of the absorber film 24, a highly precise transferpattern can be formed when forming a transfer pattern on the absorberfilm 24.

[Reflective Mask 40]

The following provides an explanation of the reflective mask 40according to one embodiment of the present invention.

FIG. 4 is a schematic diagram showing the reflective mask 40 of thepresent embodiment.

The reflective mask 40 of the present invention employs a configurationin which the absorber pattern 27 is formed on the aforementionedmultilayer reflective film 21 or the aforementioned protective film 22by pattering the absorber film 24 on the aforementioned reflective maskblank 30. When the reflective mask 40 of the present embodiment isexposed with exposure light such as EUV light, the exposure light isabsorbed at the portion of the mask surface where the absorber film 24is present, and the exposure light is reflected by the exposedprotective film 22 and the multilayer reflective film 21 at otherportions where the absorber film 24 has been removed. Therefore, thereflective mask 40 of the present embodiment can be used as a reflectivemask 40 for lithography. According to the reflective mask 40 of thepresent invention, detection of pseudo defects in a defect inspectionusing a highly sensitive defect inspection apparatus can be inhibitedand critical defects can be made more conspicuous.

[Method of Manufacturing Semiconductor Device]

A semiconductor device, having various transfer patterns formed on atransferred substrate such as a semiconductor substrate, can bemanufactured by transferring a transfer pattern, such as a circuitpattern based on the absorber pattern 27 of the reflective mask 40, to aresist film formed on a transferred substrate such as a semiconductorsubstrate by using the previously explained reflective mask 40 and alithography process using an exposure apparatus, followed by goingthrough various other steps.

According to the method of manufacturing a semiconductor device of thepresent invention, since the reflective mask 40, which contaminants,scratches and other critical defects have been removed, can be used in adefect inspection using a highly sensitive defect inspection apparatus,there are no defects in the transfer pattern such as a circuit patterntransferred to a resist film formed on a transferred substrate such as asemiconductor substrate, and a semiconductor device can be manufacturedhaving a fine and highly precise transfer pattern.

Furthermore, fiducial marks can be formed on the previously describedmask blank substrate 10, the substrate with a multilayer reflective film20 or the reflective mask blank 30, and the coordinates of the locationsof these fiducial marks and critical defects detected with a highlysensitive defect inspection apparatus as previously described can bemanaged. When fabricating the reflective mask 40 based on the resultingcritical defect location information (defect data), drawing data can becorrected and defects can be reduced so that the absorber pattern 27 isformed at those locations where critical defects are present based onthe aforementioned defect data and transferred pattern (circuit pattern)data.

EXAMPLES

The following provides an explanation of examples of manufacturing thereflective mask blank 30 and the reflective mask 40 according to thepresent embodiment.

First, the multilayer reflective film 21 and the absorber film 24 weredeposited on the surface of the mask blank substrate 10 for EUV exposurein the manner described below to manufacture the substrate with amultilayer reflective film 20 of Example Samples 1 to 5 and ComparativeExample Samples 1 to 4.

<Fabrication of Mask Blank Substrate 10>

An SiO₂—TiO₂-based glass substrate having a size of 152 mm×152 mm and athickness of 6.35 mm was prepared for use as the mask blank substrate10, and the front and back surfaces of the glass substrate weresequentially polished with cerium oxide abrasive particles and colloidalsilica abrasive particles using a double-sided polishing apparatusfollowed by treating the surfaces with a low concentration ofhydrofluorosilicic acid. Measurement of the surface roughness of theresulting glass substrate surface with an atomic force microscopeyielded a root mean square roughness (Rms) of 0.5 nm.

The surface morphology (surface form, flatness) and total thicknessvariation (TTV) of regions measuring 148 mm×148 mm on the front and backsurfaces of the glass substrate were measured with a wavelength-shiftinginterferometer using a wavelength-modulating laser. As a result, theflatness of the front and back surfaces of the glass substrate was 290nm (convex shape). The results of measuring the surface morphology(flatness) of the glass substrate surface were stored in a computer inthe form of height information with respect to a reference surface foreach measurement point, compared with a reference value of 50 nm (convexshape) for the flatness of the front surface and a reference value of 50nm for the flatness of the back side required by glass substrates, andthe differences therewith (required removal amounts) were calculated bycomputer.

Next, processing conditions for local surface processing were setcorresponding to the required removal amounts for each processingspot-shaped region on the surface of the glass substrate. A dummysubstrate was used and preliminarily processed at a spot in the samemanner as actual processing without moving the substrate for a fixedperiod of time, the morphology thereof was measured with the samemeasuring instrument as the apparatus used to measure the surfacemorphology of the aforementioned front and back surfaces, and theprocessing volume of the spot per unit time was calculated. The scanningspeed during Raster scanning of the glass substrate was then determinedin accordance with the required removal amount obtained from the spotinformation and surface morphology information of the glass substrate.

Surface morphology was adjusted by carrying out local surface processingtreatment in accordance with the set processing conditions bymagnetorheological finishing (MRF) using a substrate finishing apparatusemploying a magnetorheological fluid so that the flatness of the frontand back surfaces of the glass substrate was not more than theaforementioned reference values. Furthermore, the magnetorheologicalfluid used at this time contained an iron component, and the polishingslurry used an alkaline aqueous solution containing about 2% by weightof an abrasive in the form of cerium oxide. Subsequently, the glasssubstrate was immersed in a cleaning tank containing an aqueoushydrochloric acid solution having a concentration of about 10%(temperature: about 25° C.) for about 10 minutes followed by rinsingwith pure water and drying with isopropyl alcohol (IPA).

Furthermore, the local processing method employed for the mask blanksubstrate 10 in the present invention is not limited to theaforementioned magnetorheological finishing. A processing method usinggas cluster ion beams (GCIB) or localized plasma may also be used.

Subsequently, surface processing by catalyst-referred etching (CARE) wascarried out after carrying out double-sided touch polishing usingcolloidal silica abrasive particles as the finishing polishing of localsurface processing treatment for the purpose of improving surfaceroughness. This CARE was carried out under the processing conditionsindicated below.

Machining fluid: Pure water

Catalyst: Platinum

Substrate rotating speed: 10.3 rpm

Catalyst surface plate rotating speed: 10 rpm

Processing time: 50 minutes

Processing pressure: 250 hPa

Subsequently, after scrubbing the edge faces of the glass substrate, theglass substrate was immersed in a cleaning tank containing aqua regia(temperature: about 65° C.) for about 10 minutes followed by rinsingwith pure water and drying. Furthermore, cleaning with aqua regia wascarried out several times until there was no longer any Pt catalystresidue on the front and back surfaces of the glass substrate.

When a 1 μm×1 μm region at an arbitrary location of the transfer patternformation region (132 mm×132 mm) on a main surface of the mask blanksubstrate 10 for EUV exposure obtained in the manner described above wasmeasured with an atomic force microscope, root mean square roughness(Rms) was determined to be 0.040 nm and maximum height (Rmax) wasdetermined to be 0.40 nm.

The power spectrum density at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹obtained by measuring a 1 μm×1 μm region on a main surface of the maskblank substrate 10 for EUV exposure obtained in the manner describedabove with an atomic force microscope was a maximum of 5.29 nm⁴ and aminimum of 1.15 nm⁴. In addition, the power spectrum density at aspatial frequency of 10 μm⁻¹ to 100 μm⁻¹ was a maximum of 1.18 nm⁴ and aminimum of 0.20 nm⁴. Thus, the power spectrum density of a main surfaceof the aforementioned mask blank substrate 10 at a spatial frequency ofnot less than 1 μm⁻¹ and at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹ canbe said to have been not more than 10 nm⁴.

A 132 mm×132 mm region on a main surface of the aforementioned maskblank substrate 10 for EUV exposure was inspected for detects using ahighly sensitive defect inspection apparatus having an inspection lightsource wavelength of 193 nm (“Teron 610” manufactured by KLA-TencorCorp.) under inspection sensitivity conditions that enabled detection ofdefects having a size of 21.5 nm in terms of sphere equivalent volumediameter (SEVD). As a result, the total number of defects, includingpseudo defects, detected was 370, and pseudo defects were inhibitedsignificantly in comparison with the more than 50,000 defectsconventionally detected. A number of detected defects of this degree(370 total defects detected) enables the presence of contaminants,scratches or other critical defects to be inspected easily.

In addition, as a result of inspecting a 132 mm×132 mm region on a mainsurface of the aforementioned mask blank substrate 10 for EUV exposurefor defects using a highly sensitive defect inspection apparatus havingan inspection light source wavelength of 266 nm (“MAGICS M7360”manufactured by Lasertec Corp.) under the most sensitive inspectionconditions, the number of defects, including pseudo defects, was lessthan 50,000 in all cases, thereby enabling inspection of criticaldefects.

Example Samples 1 to 5 and Comparative Example Samples 1 to 4

The multilayer reflective film 21 was formed on the previously describedglass substrate by alternately laminating an Mo layer (low refractiveindex layer, thickness: 2.8 nm) and an Si layer (high refractive indexlayer, thickness: 4.2 nm) (for a total of 40 laminated pairs) by ionbeam sputtering using an Mo target and Si target. When depositing themultilayer reflective film 21 by ion beam sputtering, the incident angleof sputtered Mo and Si particles relative to the normal of a mainsurface of the glass substrate in ion beam sputtering was 30 degrees andion source gas flow rate was 8 sccm.

After depositing the multilayer reflective film 21, an Ru protectivefilm 22 (film thickness: 2.5 nm) was deposited by ion beam sputtering onthe multilayer reflective film 21 in continuation therefrom to obtainthe substrate with a multilayer reflective film 20. When depositing theRu protective film 22 by ion beam sputtering, the incident angle of Rusputtered particles relative to the normal of a main surface of thesubstrate was 40 degrees and the ion source gas flow rate was 8 sccm.

Next, the absorber film 24 was deposited on a main surface of thepreviously described mask blank substrate 10 by DC magnetron sputtering.In the case of Example Samples 1 to 4 and Comparative Example Samples 1to 3, a single layer of a TaN film was used for the absorber film 24 asindicated in Table 1. In the case of Example Sample 5 and ComparativeExample Sample 4, a multilayer film composed of two layers consisting ofan absorbing layer in the form of a TaBN film and a low reflecting layerin the form of a TaBO film was used for the absorber film 24 asindicated in Table 2.

The method used to deposit the absorber film 24 (TaN film) of ExampleSamples 1 to 4 and Comparative Example Samples 1 to 3 is as describedbelow. Namely, a TaN film was deposited on a main surface of thepreviously described mask blank substrate 10 by DC magnetron sputtering.More specifically, a Ta target (multi-axis rolled target) was placed inopposition to a main surface of the mask blank substrate 10, andreactive sputtering was carried out in a mixed gas atmosphere of Ar gasand N₂ gas. Table 1 indicates the flow rates of Ar gas and N₂ gas andother deposition conditions during deposition of the TaN films ofExample Samples 1 to 4 and Comparative Example Samples 1 to 3. Followingdeposition, elementary compositions of the TaN films were measured byX-ray photoelectron spectroscopy (XPS). Table 1 indicates the elementarycompositions of the TaN films of Example Samples 1 to 4 and ComparativeExample Samples 1 to 3 as measured by XPS along with the filmthicknesses of the TaN films. Furthermore, when the crystal structure ofthe aforementioned TaN films was measured with an X-ray diffraction(XRD) analyzer, they were determined to have a microcrystallinestructure. The absorber films 24 (TaN films) of Example Samples 1 to 4and Comparative Example Samples 1 to 3 were deposited in the mannerdescribed above.

The method used to deposit the absorber film 24 (multilayer filmcomposed of two layers consisting of an absorbing layer in the form of aTaBN film and a low reflecting layer in the form of a TaBO film) ofExample Sample 5 and Comparative Example Sample 4 is as described below.Namely, an absorbing layer in the form of a TaBN film was deposited byDC magnetron sputtering on the surface of the protective film 22 of thesubstrate with a multilayer reflective film 20 that was previouslydescribed. This TaBN film was deposited by placing the substrate with amultilayer reflective film 20 in opposition to a TaB mixed sinteredtarget (Ta:B=80:20, atomic ratio) and carrying out reactive sputteringin a mixed gas atmosphere of Ar gas and N₂ gas. Table 2 indicates theflow rates of Ar gas and N₂ gas and other deposition conditions duringdeposition of the TaBN films of Example Sample 5 and Comparative ExampleSample 4. Following deposition, elementary compositions of the TaBNfilms were measured by X-ray photoelectron spectroscopy (XPS). Table 2indicates the elementary compositions of the TaBN films of ExampleSample 5 and Comparative Example Sample 4 as measured by XPS along withthe film thicknesses of the TaBN films. Furthermore, when the crystalstructure of the aforementioned TaBN films was measured with an X-raydiffraction (XRD) analyzer, they were determined to have an amorphousstructure.

In the Example Sample 5 and Comparative Example Sample 4, a TaBO film(low reflecting layer) containing Ta, B and O was then further formed onthe TaBN film by DC magnetron sputtering. Similar to the TaBN film ofthe first film, this TaBO film was deposited by placing the substratewith a multilayer reflective film 20 in opposition to a TaB mixedsintered target (Ta:B=80:20, atomic ratio) and carrying out reactivesputtering in a mixed gas atmosphere of Ar and O₂. Table 2 indicates theflow rates of Ar gas and O₂ gas and other deposition conditions duringdeposition of the TaBO films of Example Sample 5 and Comparative ExampleSample 4. Following deposition, elementary compositions of the TaBOfilms were measured by X-ray photoelectron spectroscopy (XPS). Table 2indicates the elementary compositions of the TaBO films of ExampleSample 5 and Comparative Example Sample 4 as measured by XPS along withthe film thicknesses of the TaBO films. Furthermore, when the crystalstructure of the aforementioned TaBO films was measured with an X-raydiffraction (XRD) analyzer, they were determined to have an amorphousstructure. The absorber films 24 (laminated films) of Example Sample 5and Comparative Example Sample 4 were deposited in the manner describedabove.

TABLE 1 Comparative Comparative Comparative Example Example ExampleExample Example Example Example Sample 1 Sample 2 Sample 3 Sample 4Sample 1 Sample 2 Sample 3 Target material Ta Ta Ta Ta Ta Ta TaDeposition Ar (sccm) 20 39 30 20 20 1 40 gas N₂ (sccm) 33 8 20 33 33 605 Film composition (XPS) TaN film TaN film TaN film TaN film TaN filmTaN film TaN film Ta (at %) 50 85 70 50 50 42 92 N (at %) 50 15 30 50 5058 8 Film thickness (nm) 100 100 100 50 200 100 100 Rms (nm) 0.365 0.3340.293 0.272 0.553 1.062 0.473 Maximum value of PSD 39.0 36.2 31.5 29.8114.7 197.4 53.9 (range of 1 μm⁻¹ to 10 μm⁻¹) (nm⁴) Integrated value ofPSD 497.34 475.03 452.86 439.29 1945.54 3020.11 968.72 (range of 1 μm⁻¹to 10 μm⁻¹) (×10⁻³ nm³) No. of defects detected 13204 10508 98787014 >100000 >100000 71372 (number)

TABLE 2 Comparative Example Example Sample 5 Sample 4 Absorbing Targetmaterial TaB mixed sintered target TaB mixed sintered target layer (Ta:B= 80:20, atomic (Ta:B = 80:20, atomic ratio) ratio) Deposition gas Ar(sccm) 12.4 12.4 N₂ (sccm) 6.0 6.0 Film composition (XPS) TaBN layerTaBN layer Ta (at %) 74.7 74.1 B (at %) 12.1 12.2 N (at %) 13.2 13.7Film thickness (nm) 56 186 Low Target material (Same as first film)(Same as first film) reflecting Deposition gas Ar (sccm) 57.0 57.0 layerO₂ (sccm) 28.6 28.6 Film composition (XPS) TaBO layer TaBO layer Ta (at%) 40.7 40.6 B (at %) 6.3 6.2 O (at %) 53.0 53.2 Film thickness (nm) 1414 Total film thickness (nm) 70 200 Rms (nm) 0.496 0.536 Maximum valueof PSD 46.3 44.6 (range of 1 μm⁻¹ to 10 μm⁻¹) (nm⁴) Integrated value ofPSD 752.29 875.64 (range of 1 μm⁻¹ to 10 μm⁻¹) (×10⁻³ nm³) No. ofdefects detected (number) 18572 58113

Regions measuring 3 μm×3 μm at an arbitrary location in the transferpattern formation regions (and more specifically, in the centers of thetransfer pattern formation regions) (132 mm×132 mm) were measured withan atomic force microscope for the surfaces of the absorber films 24 ofthe mask blank substrates 10 for EUV exposure obtained in the form ofExample Samples 1 to 5 and Comparative Example Samples 1 to 4. Tables 1and 2 indicate the maximum values of surface roughness (root mean squareroughness: Rms) obtained by measuring with an atomic force microscope,and power spectrum density at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹as determined by power spectrum analysis of surface roughness.

For reference purposes, FIG. 6 indicates the results of analyzing thepower spectra of Example Sample 1 and Comparative Example Sample 1. Asshown in FIG. 6, the power spectrum density at a spatial frequency of 1μm⁻¹ to 10 μm⁻¹ obtained by measuring a 3 μm×3 μm region on the surfaceof the TaN film of Example Sample 1 with an atomic force microscopedemonstrated a maximum value of 39.0 nm⁴ and a minimum value of 11.4nm⁴. On the other hand, as is also shown in FIG. 6, the power spectrumdensity at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹ obtained bymeasuring a 3 μm×3 μm region on the surface of the TaN film ofComparative Example Sample 1 with an atomic force microscopedemonstrated a maximum value of 114.7 nm⁴ and a minimum value of 34.0nm⁴.

As indicated in Tables 1 and 2, the root mean square roughness (Rms)obtained by measuring a 3 μm×3 μm region on the surface of the absorberfilm 24 of Example Samples 1 to 5 with an atomic force microscope wasnot more than 0.5 nm. On the other hand, the root mean square roughness(Rms) obtained by measuring a 3 μm×3 μm region on the surface of theabsorber film 24 of Comparative Example Samples 1, 2 and 4 with anatomic force microscope was greater than 0.5 nm.

As is indicated in Tables 1 and 2, the maximum value of power spectrumdensity at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹ of the surface ofthe absorber film 24 of Example Samples 1 to 5 was not more than 50 nm⁴.On the other hand, the maximum value of power spectrum density at aspatial frequency of 1 μm⁻¹ to 10 μm⁻¹ of the surface of the absorberfilm 24 of Comparative Example Samples 1 to 3 was greater than 50 nm⁴.

Regions measuring 132 mm×132 mm on the surface of the absorber film 24of Example Samples 1 to 5 and Comparative Example Samples 1 to 4 wereinspected for detects under inspection sensitivity conditions enablingdetection of defects having a sphere equivalent volume diameter (SEVD)of 21.5 nm using a highly sensitive defect inspection apparatus havingan inspection light source wavelength of 193 nm (“Teron 610”manufactured by KLA-Tencor Corp.). Furthermore, sphere equivalent volumediameter (SEVD) can be calculated according to the equation:SEVD=2(3S/4πh)^(1/3) when defining (S) to be the area of the defect anddefining (h) to be the defect height. Defect area (S) and defect height(h) can be measured with an atomic force microscope (AFM).

Tables 1 and 2 indicate the number of defects detected, including pseudodefects, in the surface of the absorber films 24 of Example Samples 1 to5 and Comparative Example Samples 1 to 4 as determined by measuring thesphere equivalent volume diameter (SEVD). The maximum total number ofdefects detected in Example Samples 1 to 5 was 18,572 (Example Sample5), indicating that the number of pseudo defects was significantlyinhibited in comparison with the more than 50,000 defects conventionallydetected. A total of 18,572 detected defects means that the presence orabsence of contaminants, scratches and other critical defects can beinspected easily. In contrast, the minimum total number of defectsdetected in Comparative Example Samples 1 to 4 was 58,111 (ComparativeExample Sample 4), indicating that inspections were unable to be carriedout for the presence or absence of contaminants, scratches or othercritical defects.

<Fabrication of Reflective Mask Blank 30: Examples 1 and 2 andComparative Examples 1 and 2>

Reflective mask blanks 30 of Examples 1 and 2 and Comparative Examples 1and 2 were fabricated under the conditions shown in Table 3. Namely,similar to the cases of Example Samples 1 to 5 and Comparative ExampleSamples 1 to 4, the multilayer reflective film 21 was formed on thesurface of the mask blank substrate 10 for EUV exposure. Subsequently,the protective film 22 was deposited on the surface of the multilayerreflective film 21, and the absorber film 24 shown in Table 3 wasdeposited on the protective film 22. Moreover, the back sideelectrically conductive film 23 was deposited on the mask blanksubstrate 10 to fabricate the reflective mask blanks 30 of Examples 1and 2 and Comparative Examples 1 and 2.

TABLE 3 Comparative Comparative Example 1 Example 2 example 1 example 2Absorber film Same as Same as Same as Same as Example Sample ExampleSample Comparative Comparative 3 (TaN film) 5 (TaBN Example SampleExample Sample layer/TaBO 2 (TaN film) 3 (TaN film) layer) Absorber filmthickness (nm) 85 85 85 85 Back side electrically CrN film CrN film CrNfilm CrN film conductive film Back side electrically 20 20 20 20conductive film thickness (nm) Rms (nm) 0.285 0.498 0.98 0.459 Maximumvalue of PSD 30.7 46.9 178.2 52.1 (range of 1 μm⁻¹ to 10 μm⁻¹) (nm⁴)Integrated value of PSD 450.56 768.21 2547.30 939.48 (range of 1 μm⁻¹ to10 μm⁻¹) (×10⁻³ nm³) No. of defects detected 8570 19986 >100000 69950(number)

Furthermore, fiducial marks for managing coordinates of the locations ofthe aforementioned defects were formed with a focused ion beam at 4locations outside the transfer pattern formation region (132 mm×132 mm)on the protective film 22 and the multilayer reflective film 21 of thesubstrate with a multilayer reflective film 20 used in Examples 1 and 2and Comparative Examples 1 and 2.

The back side electrically conductive film 23 was formed in the mannerdescribed below. Namely, the back side electrically conductive film 23was formed by DC magnetron sputtering on the back side of the substratewith a multilayer reflective film 20 used in Examples 1 and 2 andComparative Examples 1 and 2 where the multilayer reflective film 21 wasnot formed. The back side electrically conductive film 23 was formed bypositioning a Cr target in opposition to the back side of the substratewith a multilayer reflective film 20 and carrying out reactivesputtering in an atmosphere consisting of a mixture of Ar and N₂ gas(Ar:N₂=90%:10%). Measurement of the elementary composition of the backside electrically conductive film 23 by Rutherford back scatteringanalysis yielded values of 90 at % for Cr and 10 at % for N. Inaddition, the film thickness of the back side electrically conductivefilm 23 was 20 nm. The reflective mask blanks 30 of Examples 1 and 2 andComparative Examples 1 and 2 were fabricated in the manner describedabove.

Regions measuring 3 μm×3 μm at arbitrary locations of the transferpattern formation regions (132 mm×132) (and more specifically, thecenters of the transfer pattern regions) on the surfaces of the absorberfilms 24 of the reflective mask blanks 30 of Examples 1 and 2 andComparative Examples 1 and 2 were measured with an atomic forcemicroscope. Table 3 indicates the values of surface roughness (root meansquare roughness, Rms) obtained by measuring with an atomic forcemicroscope and the maximum values of power spectrum density (PSD) at aspatial frequency of 1 μm⁻¹ to 10 μm⁻¹ determined by power spectrumanalysis of surface roughness.

As shown in Table 3, the root mean square roughness (Rms) obtained bymeasuring a 3 μm×3 μm region on the surface of the absorber film 24 ofthe reflective mask blanks 30 of Examples 1 and 2 with an atomic forcemicroscope was not more than 0.5 nm. On the other hand, the root meansquare roughness (Rms) obtained by measuring a 3 μm×3 μm region on thesurface of the absorber film 24 of the reflective mask blank 30 ofComparative Example 1 with an atomic force microscope was greater than0.5 nm.

As is also shown in Table 3, the maximum value of the power spectrumdensity at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹ of the surface ofthe absorber films 24 of Examples 1 and 2 was not more than 50 nm⁴. Onthe other hand, the maximum value of the power spectrum density at aspatial frequency of 1 μm⁻¹ to 10 μm⁻¹ of the surface of the absorberfilms 24 of Comparative Examples 1 and 2 was greater than 50 nm⁴.

Regions measuring 132 mm×132 mm on the surfaces of the absorber films 24of Example Samples 1 to 5 and Comparative Example Samples 1 to 4 wereinspected for detects using a highly sensitive defect inspectionapparatus having an inspection light source wavelength of 193 nm (“Teron610” manufactured by KLA-Tencor Corp.) under inspection sensitivityconditions that enabled detection of defects having a size of 21.5 nm interms of sphere equivalent volume diameter (SEVD). Furthermore, sphereequivalent volume diameter (SEVD) can be calculated according to theequation: SEVD=2(3S/4πh)^(1/3) when defining (S) to be the area of thedefect and defining (h) to be the defect height. Defect area (S) anddefect height (h) can be measured with an atomic force microscope (AFM).

Table 3 indicates the number of defects detected, including pseudodefects, in the surface of the absorber films 24 of Examples 1 and 2 andComparative Examples 1 and 2 as determined by measuring the sphereequivalent volume diameter (SEVD). The maximum total number of defectsdetected in Examples 1 and 2 was 19,986 (Example 2), indicating that thenumber of pseudo defects was significantly inhibited in comparison withthe more than 50,000 defects conventionally detected. A total of 19,986detected defects means that the presence or absence of contaminants,scratches and other critical defects can be inspected easily. Incontrast, the minimum total number of defects detected in ComparativeExamples 1 and 2 was 69,950 (Comparative Example 2), indicating thatinspections were unable to be carried out for the presence or absence ofcontaminants, scratches or other critical defects.

<Fabrication of Reflective Mask 40>

The surface of the absorber film 24 of the reflective mask blanks 30 ofExamples 1 and 2 and Comparative Examples 1 and 2 were coated withresist by spin coating and a resist film 25 having a film thickness of150 nm was deposited thereon after going through heating and coolingsteps. Next, a resist pattern was formed by going through desiredpattern drawing and developing steps. An absorber pattern 27 on theprotective film 22 was formed by patterning of absorber film 24 with aprescribed dry etching using the resist pattern as a mask. Furthermore,in the case the absorber film 24 consists of a TaBN film, dry etchingcan be carried out with a mixed gas of Cl₂ and He. In addition, in thecase the absorber film 24 consists of a laminated film composed of twolayers consisting of a TaBN film and a TaBO film, dry etching can becarried out with a mixed gas of chlorine (Cl₂) and oxygen (O₂) (mixingratio (flow rate ratio) of chlorine (Cl₂) to oxygen (O₂)=8:2).

Subsequently, the resist film 25 was removed followed by chemicalcleaning in the same manner as previously described to fabricate thereflective masks 40 of Examples 1 and 2 and Comparative Examples 1 and2. Furthermore, the reflective masks 40 were fabricated after correctingdrawing data in the aforementioned drawing step so that the absorberpattern 27 was arranged at locations where critical defects are presentbased on defect data and transferred pattern (circuit pattern), and thedefect data is generated in reference to the aforementioned fiduciarymarks. Defect inspections were carried out on the resulting reflectivemasks 40 of Examples 1 and 2 and Comparative Examples 1 and 2 using ahighly sensitive defect inspection apparatus (“Teron 610” manufacturedby KLA-Tencor Corp.).

Defects were not confirmed during measurement with the highly sensitivedefect inspection apparatus in the case of the reflective masks 40 ofExamples 1 and 2. On the other hand, in the case of the reflective masks40 of Comparative Examples 1 and 2, a large number of defects duringmeasurement with the highly sensitive defect inspection apparatus.

<Fabrication of Reflective Mask Blank 30 Having an Absorber Film with aPhase Shift Function Formed Thereon>

The reflective mask blanks 30 of Examples 3 to 5 were fabricated underthe conditions shown in Table 4. Similar to the cases of Example Samples1 to 5 and Comparative Example Samples 1 to 4, the multilayer reflectivefilm 21 was deposited on the surface of the mask blank substrate 10 forEUV exposure. Subsequently, the protective film 22 was deposited on thesurface of the multilayer reflective film 21 and the absorber film 24shown in Table 4 was deposited on the protective film 22. Morespecifically, the absorber film 24 was formed by laminating a tantalumnitride film (TaN film) and a chromium carbooxonitride film (CrCON film)by DC sputtering. The TaN films were formed in the manner indicatedbelow. Namely, TaN films (Ta: 85 at %, N: 15 at %) having the filmthicknesses described in Table 4 were formed by reactive sputtering in amixed gas atmosphere of Ar gas and N₂ gas using a tantalum target. TheCrCON films were formed in the manner indicated below. Namely, CrCONfilms (Cr: 45 at %, C: 10 at %, O: 35 at %, N: 10 at %) having the filmthicknesses described in Table 4 were formed by reactive sputtering in amixed gas atmosphere of Ar gas, CO₂ gas and N₂ gas using a chromiumtarget. Moreover, similar to Examples 1 and 2, the reflective maskblanks 30 of Examples 3 to 5 were fabricated by depositing the back sideelectrically conductive film 23 on the back side of the mask blanksubstrate 10.

TABLE 4 Example 3 Example 4 Example 5 Absorber film lower layer (filmthickness) TaN (54.3 nm) TaN (48.9 nm) TaN (33.4 nm) Absorber film upperlayer (film thickness) CrCON (5 nm) CrCON (10 nm) CrCON (25 nm) Absorberfilm total thickness (nm) 59.3 58.9 58.4 EUV absolute reflectance (%)2.4 2.9 3.6 RMS (nm) 0.242 0.236 0.355 Maximum value of Range of 1 μm⁻¹28.9 44.4 33.4 PSD (nm⁴) to 10 μm⁻¹ Integrated value of Range of 1 μm⁻¹433.2 467.9 555.4 PSD (×10⁻³ nm³) to 10 μm⁻¹ No. of defects detected(number) 6254 10094 25212

Regions measuring 3 μm×3 μm in the centers of the transfer patternformation regions on the surfaces of the absorber film 24 of thereflective mask blanks of Examples 3 to 5 were measured with an atomicforce microscope, in the same manner as Examples 1 and 2. Table 4indicates the maximum values of surface roughness (root mean squareroughness: Rms) obtained by measuring with an atomic force microscopeand power spectrum density (PSD) at a spatial frequency of 1 μm⁻¹ to 10μm⁻¹ as determined by power spectrum analysis of surface roughness.

As shown in Table 4, the root mean square roughness (Rms) obtained bymeasuring a 3 μm×3 μm region on the surface of the absorber film 24 ofthe reflective mask blanks 30 of Examples 3 to 5 with an atomic forcemicroscope was favorable at not more than 0.5 nm.

In addition, the maximum value of power spectrum density at a spatialfrequency of 1 μm⁻¹ to 10 μm⁻¹ of the surface of the absorber film 24 ofExamples 3 to 5 was not more than 50 nm⁴ and the integrated value wasalso favorable at not more than 800×10⁻³ nm³.

Next, regions measuring 132 mm×132 mm on the surface of the absorberfilms 24 of Examples 3 to 5 were inspected for detects under inspectionsensitivity conditions enabling detection of defects having a sphereequivalent volume diameter (SEVD) of 21.5 nm using a highly sensitivedefect inspection apparatus having an inspection light source wavelengthof 193 nm (“Teron 610” manufactured by KLA-Tencor Corp.) in the samemanner as Examples 1 and 2.

As a result, the number of defects detected on the surface of theabsorber film 24 of Example 3 was the lowest at 6,254, and was followedby the absorber film 24 of Example 4 at 10,094 defects and the absorberfilm 24 of Example 5 at 25,212 defects, thus indicating that the numberof defects detected was of a level that enables the presence or absenceof contaminants, scratches or other critical defects to be inspectedeasily.

<Method of Manufacturing Semiconductor Device>

When semiconductor devices were fabricated using the reflective masks 40of the aforementioned Examples 1 to 4 and Comparative Examples 1 and 2and carrying out pattern transfer on a resist film on a transferredsubstrate in the form of a semiconductor substrate using an exposureapparatus followed by patterning an interconnection layer, semiconductordevices were able to be fabricated that were free of pattern defects.

Furthermore, in fabricating the previously described substrate with amultilayer reflective film 20 and the reflective mask blank 30, althoughthe multilayer reflective film 21 and the protective film 22 weredeposited on a main surface of the mask blank substrate 10 on the sidewhere a transfer pattern is formed followed by forming the back sideelectrically conductive film 23 on the opposite side from theaforementioned main surface, fabrication is not limited thereto. Thereflective mask blank 30 may also be fabricated by forming the back sideelectrically conductive film 23 on a main surface of the mask blanksubstrate 10 on the opposite side from the main surface on the side onwhich a transfer pattern is formed, followed by depositing themultilayer reflective film 21 and the protective film 22 on the mainsurface on the side where the transfer pattern is formed, and finallydepositing the absorber film 24 on the substrate with a multilayerreflective film 20 and the protective film 22.

BRIEF DESCRIPTION OF THE REFERENCE SYMBOLS

10 Mask blank substrate

20 Substrate with a multilayer reflective film

21 Multilayer reflective film

22 Protective film

23 Back side electrically conductive film

24 Absorber film

25 Etching mask film

26 Mask blank multilayer film

27 Absorber pattern

30 Reflective mask blank

40 Reflective mask

The invention claimed is:
 1. A reflective mask blank, comprising: a maskblank multilayer film that comprises a multilayer reflective filmobtained by alternately laminating a high refractive index layer and alow refractive index layer, and an absorber film on or above a mainsurface of a mask blank substrate; wherein, the root mean squareroughness (Rms), obtained by measuring a 3 μm×3 μm region on a surfaceof the reflective mask blank on which the mask blank multilayer film isformed with an atomic force microscope, is not more than 0.5 nm and thepower spectrum density at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹ isnot more than 50 nm⁴.
 2. The reflective mask blank according to claim 1,wherein the mask blank multilayer film further comprises a protectivefilm arranged in contact with a surface of the multilayer reflectivefilm on the opposite side from the mask blank substrate.
 3. Thereflective mask blank according to claim 1, wherein the mask blankmultilayer film further comprises an etching mask film arranged incontact with the surface of the absorber film on the opposite side fromthe mask blank substrate.
 4. The reflective mask blank according toclaim 1, wherein the absorber film comprises tantalum and nitrogen, andthe nitrogen content is 10 at % to 50 at %.
 5. The reflective mask blankaccording to claim 1, wherein the film thickness of the absorber film isnot more than 60 nm.
 6. The reflective mask blank according to claim 1,wherein the absorber film has a phase shift function by which the phasedifference between light reflected from the surface of the absorber filmand light reflected from the surface of the multilayer reflective filmor protective film where the absorber film is not formed has aprescribed phase difference.
 7. A reflective mask having an absorberpattern, obtained by patterning the absorber film of the reflective maskblank according to claim 1, on the multilayer reflective film.
 8. Amethod of manufacturing a reflective mask blank having a mask blankmultilayer film comprising a multilayer reflective film and an absorberfilm on or above a main surface of a mask blank substrate, wherein amultilayer reflective film is obtained by alternately laminating a highrefractive index layer and a low refractive index layer, the methodcomprising: forming the multilayer reflective film on or above the mainsurface of the mask blank substrate, and forming the absorber film on orabove the multilayer reflective film; wherein, the absorber film isformed so that a surface of the reflective mask blank has a root meansquare roughness (Rms), obtained by measuring a 3 μm×3 μm region with anatomic force microscope, of not more than 0.5 nm and a power spectrumdensity at a spatial frequency of 1 μm⁻¹ to 10 μm⁻¹ of not more than 50nm⁴.
 9. The method of manufacturing a reflective mask blank according toclaim 8, wherein, when the multilayer reflective film is formed, themultilayer reflective film is formed by ion beam sputtering byalternately irradiating a sputtering target of a high refractive indexmaterial and a sputtering target of a low refractive index material withan ion beam.
 10. The method of manufacturing a reflective mask blankaccording to claim 8, when the absorber film is formed, the absorberfilm is formed by reactive sputtering using a sputtering target of anabsorber film material, the absorber film is formed so as to contain acomponent contained in the atmospheric gas during reactive sputtering,and the flow rate of the atmospheric gas is controlled so that the rootmean square roughness (Rms) is not more than 0.5 nm and the powerspectrum density is not more than 50 nm⁴.
 11. The method ofmanufacturing a reflective mask blank according to claim 10, wherein theatmospheric gas is a mixed gas containing an inert gas and nitrogen gas.12. The method of manufacturing a reflective mask blank according toclaim 8, wherein the absorber film is formed using a sputtering targetof a material containing tantalum.
 13. The method of manufacturing areflective mask blank according to claim 8, wherein, when the absorberfilm is formed, the absorber film is formed by sputtering using asputtering target of a material of the absorber film, and the materialand film thickness of the absorber film are selected so that the surfaceof the absorber film has a root mean square roughness (Rms) of not morethan 0.5 nm and a power spectrum density at a spatial frequency of 1μm⁻¹ to 10 μm⁻¹ of not more than 50 nm⁴.
 14. The method of manufacturinga reflective mask blank according to claim 13, wherein the material ofthe absorber film is a material that contains nitrogen, and the filmthickness of the absorber film is not more than 60 nm.
 15. The method ofmanufacturing a reflective mask blank according to claim 8, furthercomprising forming a protective film arranged in contact with thesurface of the multilayer reflective film.
 16. The method ofmanufacturing a reflective mask blank according to claim 15, wherein theprotective film is formed by ion beam sputtering by irradiating asputtering target of a protective film material with an ion beam. 17.The method of manufacturing a reflective mask blank according to claim8, further comprising forming an etching mask film arranged in contactwith the surface of the multilayer reflective film.
 18. A method ofmanufacturing a semiconductor device, comprising: forming a transferpattern on a transferred substrate by carrying out a lithography processwith an exposure apparatus using the reflective mask according to claim7.